Self-administered sphenopalatine ganglion blocks are extremely helpful for treatment of migraines, chronic daily headaches, anxiety and temporomandibular joint disorders.  Neuromuscular dentistry and the role of the autonomic nervous system: Sphenopalatine ganglion blocks and neuromodulation. An International College of Cranio Mandibular Orthopedics (ICCMO) position paper  They are also effective in about  1 ⁄ 3  of cases of essential hypertension. Bilateral sphenopalatine ganglion block reduces blood pressure in never treated patients with essential hypertension. A randomized controlled single-blinded study


The sphenopalatine ganglion block has been called "The Miracle Block" after publication of Albert Bengamin Gerber's book  Miracles on Park Avenue , the story of octogenerian otorhinolargyngologist Dr. Milton Reder, whose entire medical practice was based on that procedure. [ citation needed ]


There are multiple new devices utilized for neuromodulation of the sphenopalatine ganglion.  There is one non-invasive device, a myomonitor, an ultra low frequency transcutaneous electrical nerve stimulation that has been utilized safely for more than 50 years by neuromuscular dentists in the diagnosis and treatment of temporomandibular joint disorders and orofacial pain conditions.  Spenopalatine ganglion neuromodulation (possibly via the vagal nerve) is a secondary effect making it extremely effective for TMD. Neuromuscular dentistry and the role of the autonomic nervous system: Sphenopalatine ganglion blocks and neuromodulation. An International College of Cranio Mandibular Orthopedics (ICCMO) position paper


This article incorporates text in the  public domain  from  page 891  of the 20th edition of   Gray's Anatomy   (1918)


Reconstructive surgery  is  surgery  performed to restore normal appearance and function to body parts malformed by a disease or medical condition.


Reconstructive surgery is a term with training, clinical, and reimbursement implications. It has historically been referred to as synonymous with  plastic surgery . [ 1 ]  In regard to training,  plastic surgery  is a recognized medical specialty and a surgeon can be a "board-certified" plastic surgeon by the  American Board of Plastic Surgery . [ 2 ]  However, reconstructive surgery is not a specialty and there are no board-certified reconstructive surgeons.


More accurately, reconstructive surgery should be contrasted with  cosmetic surgery . Reconstructive surgery is performed to


Separately, the patient must be healthy enough so that the benefits of the procedure outweigh the risks of complications or death. A procedure could be considered reconstructive but not medically necessary due to the risk to the patient.


In addition, Section 1862(a) (1) (A) of the Social Security Act directs the following:
"No payment may be made under Part A or Part B for any expenses incurred for items or services not reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member." [ 4 ]  Therefore, outside clinical interpretation and carrier guidelines, there is a federal statute that "improving functionality and restoring appearance" are covered as reconstructive and medically necessary. [ 5 ]


This definition is contrasted with cosmetic surgery performed to improve aesthetics or the appearance of a body part. [ 6 ]  A plastic surgeon can perform both reconstructive and cosmetic procedures. Some procedures, such as a panniculectomy (aka tummy tuck) can be considered as cosmetic by one insurance company and reconstructive by another. The surgeon may not be using the Medicare or reimbursement criteria when referring to a procedure as reconstructive or cosmetic. Plastic surgeons,  maxillo-facial surgeons  and  otolaryngologists  do reconstructive surgery on faces to correct congenital defects, after trauma and to reconstruct the head and neck after cancer. [ 7 ]


Another good example is repair of a cleft palate, or cheiloplasty, which surgically corrects abnormal development, restores function to the lips and mouth and produces a more normal appearance. [ 8 ]  This meets the definition of reconstructive surgery and is mandated by state laws in at least 31 states, but could be denied as cosmetic by individual insurance companies in the remaining  states. [ 9 ]


Other branches of surgery ( e.g. ,  general surgery ,  gynecological surgery ,  pediatric surgery ,  plastic surgery ,  podiatric surgery ) also perform some reconstructive procedures.


Reconstructive surgery represents a small but critical component of the comprehensive care of cancer patients. Its primary role in the treatment of cancer patients is to extend the ability of other surgeons and specialists to more radically treat cancer, offering patients the best opportunity for cure. [ 10 ]


Reconstructive surgeons use the concept of a  reconstructive ladder  to manage increasingly complex wounds. This ranges from very simple techniques such as primary closure and dressings to more complex skin grafts, tissue expansion, and free flaps. [ citation needed ]


Reconstructive surgery procedures include breast implant removal, reduction mammoplasty, breast reconstruction, surgical correction of birth anomalies, congenital nevi surgery, and liposuction for  lipedema . [ 11 ] [ 12 ]
Cosmetic surgery procedures include  breast enhancement , reduction and lift,  face lift ,  forehead lift , upper and lower eyelid surgery ( blepharoplasty ), laser skin resurfacing ( laser resurfacing ),  chemical peel , nose reshaping ( rhinoplasty ), reconstruction  liposuction ,  Nasal reconstruction using a paramedian forehead flap , as well as  tummy tuck  ( abdominoplasty ). [ 13 ]


Recent literature in  medline  also has noted implementation of  barbed suture  in these procedures. [ 14 ]


Biomaterials are, in their simplest form, plastic implants used to correct or replace damaged body parts. Biomaterials were not used for reconstructive purposes until after  World War II  due to the new and improved technology and the tremendous need for the correction of damaged body parts that could replace  transplantation . The process involves scientific and medical research to ensure that the biomaterials are  biocompatible  and that they can assume the mechanical and functioning roles of the components they are replacing. [ citation needed ]


A successful implantation can best be achieved by a team that understands not only the  anatomical ,  physiological ,  biochemical , and  pathological  aspects of the problem, but also comprehends  bioengineering . Cellular and tissue engineering is crucial to know for reconstructive procedures. [ 15 ]


An overview of the standardization and control of  biomedical  devices has recently been gathered by D. G. Singleton. Papers have covered in depth the U.S.  Food and Drug Administration  (FDA) Premarket Approval Process (J. L. Ely) and FDA regulations governing Class III devices. Two papers have described how the  National Institute of Standards and Technology ,  American Dental Association ,  National Institute of Dental and Craniofacial Research , and private dental companies have collaborated in a number of important advances in dental materials, devices, and analytical systems. [ citation needed ]


Restylane  is the trade name for a range of  injectable fillers  with a specific formulation of  hyaluronic acid  (HA).


In the  United States , Restylane was the first hyaluronic acid filler to be approved by the  U.S. Food and Drug Administration  (FDA) for cosmetic injection into subdermal facial tissues. [ 1 ]


Restylane is produced by  Galderma .


Restylane is most commonly used for  lip enhancement  (volume and contouring). It is used to diminish  wrinkles  and aging lines of the face such as the  nasolabial folds  (nose to mouth lines) and melomental folds (sad mouth corners).  It may also be used for filling aging-related facial hollows and "orbital troughs" (under and around the eyes), as well as for cheek volume and contouring of the chin, lips and nose. [ 2 ]


A treatment with a dermal filler like Restylane can cause some temporary bruising in addition to
swelling and numbness for a few days. In rare cases there has been reports of lumps or granulomas. These side effects can be easily reversed with a treatment of  hyaluronidase , which is an enzyme that speeds up the natural degradation of the injected hyaluronic acid filler. [ 3 ]


Several studies have been done to understand the long-term side effects of restylane and other hyaluronic acid fillers. [ 4 ]  In certain cases, the filler results in a granulomatous foreign body reaction. [ 4 ] [ 5 ]


Even though side effects are rare Restylane should not be used in or near areas where there is or has been skin disease, inflammation or related conditions. Restylane has not been tested in pregnant or breast-feeding women.


Restylane dermal fillers are generally considered safe, there are certain contraindications and safety rules that online licensed providers should be aware of before buying and injecting Restylane fillers.


Contraindications for Restylane dermal fillers:


Most injectors inject the filler with a small needle under the skin. Numbing creams or injections decrease pain.


A new way to use Restylane was described in the August 2007 issue of the  Journal of Drugs in Dermatology  by  Dutch  cosmetic doctor Tom van Eijk, whose "fern pattern" injection technique aims to restore dermal elasticity rather than to fill underneath the wrinkles. [ 6 ]


Mimic wrinkles are inextricably linked to the skin and affect the formation of fine wrinkles. Muscles woven into the dermis, contracting, tighten the skin, which provides mimic facial mobility. Their constant movement stretches the skin and leads to its sagging. This drug helps to restore weakened tissue and increase its volume without external damage. [ citation needed ]


The  retromandibular vein  ( temporomaxillary vein ,  posterior facial vein ) is a major vein of the face. It is formed within the parotid gland by the confluence of the  maxillary vein , and  superficial temporal vein . It descends in the gland and splits into two branches upon emerging from the gland. Its  anterior branch  then joins the  (anterior) facial vein  forming the  common facial vein , while its  posterior branch  joins the  posterior auricular vein  forming the  external jugular vein .


The retromandibular vein is formed within the  parotid gland [ 1 ]  by the confluence of the  maxillary vein , and  superficial temporal vein . [ 1 ] [ 2 ] [ 3 ]


It descends inside  parotid gland , [ 1 ] [ 4 ]  superficial to the  external carotid artery  (but beneath the  facial nerve ), [ 4 ]  between the  sternocleidomastoideus  muscle and  ramus of mandible . [ citation needed ]  It emerges from the parotid gland inferiorly, then immediately divides into two branches: [ 1 ]


The retromandibular vein provides venous drainage to the superior  cranium , and significant drainage to the  ear . [ 7 ]


Parrot's sign  is a sensation of pain when pressure is applied to the retromandibular region. [ citation needed ]


This article incorporates text in the  public domain  from  page 646  of the 20th edition of   Gray's Anatomy   (1918)


Retropharyngeal abscess  ( RPA ) is an  abscess  located in the tissues in the back of the throat behind the posterior pharyngeal wall (the  retropharyngeal space ).  Because RPAs typically occur in deep tissue, they are difficult to diagnose by  physical examination  alone. RPA is a relatively uncommon illness, and therefore may not receive early diagnosis in children presenting with  stiff neck ,  malaise ,  difficulty swallowing , or other symptoms listed below. Early diagnosis is key, while a delay in diagnosis and treatment may lead to death.  Parapharyngeal space  communicates with retropharyngeal space and an infection of retropharyngeal space can pass down behind the  esophagus  into the  mediastinum . [ 1 ]  RPAs can also occur in adults of any age.


RPA can lead to  airway obstruction  or  sepsis  – both life-threatening emergencies. [ 2 ]  Fatalities normally occur from patients not receiving treatment immediately and suffocating prior to knowing that anything serious was wrong.


Signs and symptoms may include the following  stiff neck  (limited neck mobility or  torticollis ), [ 3 ]  some form of  palpable  neck pain (may be in "front of the neck" or around the  Adam's apple ),  malaise , difficulty swallowing,  fever ,  stridor , drooling,  croup -like cough or enlarged cervical  lymph nodes . Any combination of these symptoms should arouse suspicion of RPA. [ citation needed ]


RPA is usually caused by a bacterial infection originating from the  nasopharynx ,  tonsils ,  sinuses ,  adenoids ,  molar teeth  or  middle ear . Any  upper respiratory infection  (URI) can be a cause. RPA can also result from a direct infection due to penetrating injury or a  foreign body . RPA can also be linked to young children who do not have adequate dental care or brush their teeth properly. [ citation needed ]


A computed tomography (CT) scan is the definitive diagnostic imaging test. [ 4 ]


X-ray of the neck often (80% of the time) shows swelling of the retropharyngeal space in affected individuals. If the  retropharyngeal space  is more than half of the size of the C2 vertebra, it may indicate retropharyngeal abscess. [ 5 ]


RPA's frequently require surgical intervention. A  tonsillectomy  approach is typically used to access/drain the abscess, and the outcome is usually positive. Surgery in adults may be done without general anesthesia because there is a risk of abscess rupture during tracheal intubation. This could result in  pus  from the abscess aspirated into the lungs. In complex cases, an emergency tracheotomy may be required to prevent upper airway obstruction caused by edema in the neck. [ citation needed ]


High-dose intravenous  antibiotics  are required in order to control the infection and reduce the size of the abscess prior to surgery. Chronic retropharyngeal abscess is usually secondary to  tuberculosis  and the patient needs to be started on anti-tubercular therapy as soon as possible. [ citation needed ]


Rhinitis , also known as  coryza , [ 3 ]  is irritation and  inflammation  of the  mucous membrane  inside the  nose . Common symptoms are a  stuffy nose ,  runny nose ,  sneezing , and  post-nasal drip . [ 4 ]


The inflammation is caused by  viruses ,  bacteria , irritants or  allergens . The most common kind of rhinitis is  allergic rhinitis , [ 5 ]  which is usually triggered by airborne  allergens  such as  pollen  and  dander . [ 6 ]  Allergic rhinitis may cause additional symptoms, such as sneezing and nasal itching,  coughing ,  headache , [ 7 ]   fatigue ,  malaise , and  cognitive impairment . [ 8 ] [ 9 ]  The allergens may also affect the eyes, causing watery, reddened, or itchy eyes and puffiness around the eyes. [ 7 ]  The inflammation results in the generation of large amounts of  mucus , commonly producing a runny nose, as well as a stuffy nose and post-nasal drip. In the case of allergic rhinitis, the inflammation is caused by the  degranulation  of  mast cells  in the nose. When mast cells degranulate, they release  histamine  and other chemicals, [ 10 ]  starting an inflammatory process that can cause symptoms outside the nose, such as fatigue and malaise. [ 11 ]  In the case of infectious rhinitis, it may occasionally lead to  pneumonia , either  viral  or  bacterial . Sneezing also occurs in infectious rhinitis to expel bacteria and viruses from the respiratory tract.


Rhinitis is very common. Allergic rhinitis is more common in some countries than others; in the United States, about 10–30% of adults are affected annually. [ 12 ]  Mixed rhinitis (MR) refers to patients with nonallergic rhinitis and allergic rhinitis. MR is a specific rhinitis subtype. It may represent between 50 and 70% of all AR patients. However, true prevalence of MR has not been confirmed yet. [ 13 ]


Rhinitis is categorized into three types (although infectious rhinitis is typically regarded as a separate clinical entity due to its transient nature): (i) infectious rhinitis includes acute and chronic  bacterial infections ; (ii)  nonallergic rhinitis [ 14 ]  includes vasomotor, idiopathic,  hormonal ,  atrophic , occupational, and  gustatory rhinitis , as well as  rhinitis medicamentosa  (rebound congestion); (iii)  allergic rhinitis , triggered by  pollen ,  mold , animal  dander , dust,  Balsam of Peru , and other inhaled allergens. [ 15 ]


Rhinitis is commonly caused by a  viral  or  bacterial  infection, including the common cold, which is caused by  Rhinoviruses ,  Coronaviruses , and  influenza viruses , others caused by  adenoviruses ,  human parainfluenza viruses ,  human respiratory syncytial virus ,  enteroviruses  other than rhinoviruses,  metapneumovirus , and  measles virus , or bacterial  sinusitis , which is commonly caused by  Streptococcus pneumoniae ,  Haemophilus influenzae , and  Moraxella catarrhalis . Symptoms of the common cold include  rhinorrhea , sneezing, sore throat ( pharyngitis ),  cough ,  congestion , and slight  headache . [ 16 ] [ citation needed ]


Nonallergic rhinitis refers to rhinitis that is not due to an allergy. The category was formerly referred to as vasomotor rhinitis, as the first cause discovered was vasodilation due to an overactive parasympathetic nerve response. As additional causes were identified, additional types of nonallergic rhinitis were recognized. Vasomotor rhinitis is now included among these under the more general classification of nonallergic rhinitis. [ 17 ]  The diagnosis is made upon excluding allergic causes. [ 18 ]  It is an umbrella term of rhinitis of multiple causes, such as occupational (chemical), smoking, gustatory, hormonal, senile (rhinitis of the elderly), atrophic, medication-induced (including rhinitis medicamentosa), local allergic rhinitis, non-allergic rhinitis with eosinophilia syndrome (NARES) and idiopathic (vasomotor or non-allergic, non-infectious perennial allergic rhinitis (NANIPER), or non-infectious non-allergic rhinitis (NINAR). [ 19 ]


In vasomotor rhinitis, [ 20 ] [ 21 ]  certain nonspecific stimuli, including changes in environment (temperature, humidity,  barometric pressure , or weather), airborne irritants (odors, fumes), dietary factors (spicy food, alcohol), sexual arousal, exercise, [ 22 ]  and emotional factors trigger rhinitis. [ 23 ]  There is still much to be learned about this, but it is thought that these non-allergic triggers cause dilation of the blood vessels in the lining of the nose, which results in swelling and drainage.


Non-allergic rhinitis can co-exist with allergic rhinitis, and is referred to as "mixed rhinitis". [ 24 ]  The pathology of vasomotor rhinitis appears to involve  neurogenic inflammation [ 25 ]  and is as yet not very well understood. The role of transient receptor potential ion channels on the non-neuronal nasal epithelial cells has also been suggested. Overexpression of these receptors have influence the nasal airway hyper-responsiveness to non-allergic irritant environmental stimuli (e.g., extremes of temperature, changes in osmotic or barometric pressure). [ 26 ]  Vasomotor rhinitis appears to be significantly more common in women than men, leading some researchers to believe that  hormone  imbalance plays a role. [ 27 ] [ 28 ]  In general, age of onset occurs after 20 years of age, in contrast to allergic rhinitis which can be developed at any age. Individuals with vasomotor rhinitis typically experience symptoms year-round, though symptoms may be exacerbated in the spring and autumn when rapid weather changes are more common. [ 17 ]  An estimated 17 million United States citizens have vasomotor rhinitis. [ 17 ]


Drinking alcohol may cause rhinitis as well as worsen  asthma  (see  alcohol-induced respiratory reactions ). In certain populations, particularly those of East Asian countries such as Japan, these reactions have a nonallergic basis. [ 29 ]  In other populations, particularly those of European descent, a genetic variant in the gene that metabolizes ethanol to acetaldehyde, ADH1B, is associated with alcohol-induced rhinitis. It is suggested that this variant metabolizes ethanol to acetaldehyde too quickly for further processing by ALDH2 and thereby leads to the accumulation of acetaldehyde and rhinitis symptoms. [ 30 ]  In these cases, alcohol-induced rhinitis may be of the  mixed rhinitis  type and, it seems likely, most cases of alcohol-induced rhinitis in non-Asian populations reflect true allergic response to the non-ethanol and/or contaminants in alcoholic beverages, particularly when these beverages are wines or beers. [ 29 ]  Alcohol-exacerbated rhinitis is more frequent in individuals with a history of rhinitis exacerbated by aspirin. [ 31 ]


Aspirin and other  non-steroidal anti-inflammatory drugs  (NSAIDs), particularly those that inhibit  cyclooxygenase 1  ( COX1 ), can worsen rhinitis and asthma symptoms in individuals with a history of either one of these diseases. [ 32 ]  These exacerbations most often appear due to  NSAID hypersensitivity reactions  rather than NSAID-induced allergic reactions. [ 33 ]


The antihistamine  azelastine , applied as a nasal spray, may be effective for vasomotor rhinitis. [ 34 ]   Fluticasone propionate  or  budesonide  (both are  steroids ) in nostril spray form may also be used for symptomatic treatment. The antihistamine  cyproheptadine  is also effective, probably due to its  antiserotonergic  effects.


A systematic review on non-allergic rhinitis reports improvement of overall function after treatment with  capsaicin  (the active component of chili peppers). The quality of evidence is low, however. [ 35 ]


Allergic rhinitis or hay fever may follow when an allergen such as  pollen , dust, or  Balsam of Peru [ 36 ]  is inhaled by an individual with a sensitized immune system, triggering  antibody  production. These antibodies mostly bind to  mast cells , which contain  histamine . When the mast cells are stimulated by an allergen, histamine (and other chemicals) are released. This causes itching, swelling, and mucus production.


Symptoms vary in severity between individuals. Very sensitive individuals can experience  hives  or other  rashes . Particulate matter in polluted air and chemicals such as  chlorine  and detergents, which can normally be tolerated, can greatly aggravate the condition. [ citation needed ]


Characteristic physical findings in individuals who have allergic rhinitis include  conjunctival  swelling and  erythema , eyelid swelling, lower eyelid  venous stasis , lateral crease on the nose, swollen nasal  turbinates , and  middle ear   effusion . [ 37 ]


Even if a person has negative  skin-prick, intradermal  and  blood tests  for allergies, they may still have allergic rhinitis, from a local allergy in the nose. This is called  local allergic rhinitis . [ 38 ]  Many people who were previously diagnosed with nonallergic rhinitis may actually have local allergic rhinitis. [ 39 ]


A  patch test  may be used to determine if a particular substance is causing the rhinitis.


Rhinitis medicamentosa is a form of drug-induced nonallergic rhinitis which is associated with  nasal congestion  brought on by the use of certain oral medications (primarily  sympathomimetic amine  and  2-imidazoline  derivatives) and  topical decongestants  (e.g.,  oxymetazoline ,  phenylephrine ,  xylometazoline , and  naphazoline   nasal sprays ) that constrict the blood vessels in the lining of the nose. [ 40 ]


Chronic rhinitis is a form of  atrophy  of the mucous membrane and glands of the nose.


Chronic form of dryness of the mucous membranes.


Chronic rhinitis associated with  polyps in the nasal cavity .


Most prominent pathological changes observed are nasal airway  epithelial  metaplasia  in which  goblet cells  replace  ciliated columnar epithelial cells  in the nasal mucous membrane. [ 26 ]  This results in mucin hypersecretion by goblet cells and decreased mucociliary activity. Nasal secretion are not adequately cleared with clinical manifestation of nasal congestion, sinus pressure, post-nasal dripping, and headache. Over-expression of transient receptor potential  (TRP) ion channels , such as TRPA1 and TRPV1, may be involved in the pathogenesis of non-allergic rhinitis. [ 41 ]


Neurogenic inflammation produced by neuropeptides released from sensory nerve endings to the airways is a proposed common mechanism of association between both allergic and non-allergic rhinitis with asthma. This may explain higher association of rhinitis with asthma developing later in life. [ 42 ]  Environmental irritants acts as modulators of airway inflammation in these contiguous airways. Development of  occupational asthma  is often preceded by occupational rhinitis. Among the causative agents are flours, enzymes used in processing food, latex, isocyanates, welding fumes, epoxy resins, and formaldehyde. Accordingly, prognosis of  occupational asthma  is contingent on early diagnosis and the adoption of protective measures for rhinitis. [ 43 ]


The different forms of rhinitis are essentially diagnosed clinically. [ clarification needed ]  Vasomotor rhinitis is differentiated from viral and bacterial infections by the lack of purulent exudate and crusting. It can be differentiated from allergic rhinitis because of the absence of an identifiable allergen. [ 44 ]


Evidence has been published from a few health  apps for mobile devices  that show potential to assist in the diagnosis of rhinitis and rhinosinusitis and to evaluate management and treatment adherence. While this shows promise for clinical management, as of 2022 [update]  few had been validated in the scientific literature, and even fewer included considerations for  multimorbidity . [ 45 ] [ 46 ]


The management of rhinitis depends on the underlying cause.


For allergic rhinitis, intranasal  corticosteroids  are recommended. [ 47 ]  For severe symptoms intranasal  antihistamines  may be added. [ 47 ]


Rhinitis is pronounced  / r aɪ ˈ n aɪ t ɪ s / , [ 48 ]  while coryza is pronounced  / k ə ˈ r aɪ z ə / . [ 49 ]


Rhinitis  comes from the  Ancient Greek   ῥίς   rhis ,  gen .:  ῥινός   rhinos , "nose".  Coryza  comes through Latin from Ancient Greek  κόρυζα . According to physician Andrew Wylie, "we use the term [ coryza ] for a cold in the head, but the two are really synonymous. The  ancient Romans  advised their patients to clean their nostrils and thereby sharpen their wits." [ 50 ]


A  facelift , technically known as a  rhytidectomy  (from the  Ancient Greek   ῥυτίς  ( rhytis ) 'wrinkle', and  ἐκτομή  ( ektome ) 'excision', the surgical removal of wrinkles), is a type of  cosmetic surgery  procedure intended to give a more youthful facial appearance. There are multiple surgical techniques and exercise routines. Surgery usually involves the removal of excess facial skin, with or without the tightening of underlying tissues, and the redraping of the  skin  on the  patient 's  face  and  neck . Exercise routines tone underlying facial muscles without surgery. Surgical facelifts are effectively combined with eyelid surgery ( blepharoplasty ) and other facial procedures and are typically performed under general anesthesia or deep  twilight sleep .


According to the most recent American Society for Aesthetic Plastic Surgery facelifts were the third most popular aesthetic surgery in 2019, surpassed only by  rhinoplasty  and  blepharoplasty . [ 1 ]


Cost varies by country where surgery is performed. Prices were quoted ranging from US$2,500 ( India  and  Panama ) to US$15,000 ( United States  and  Canada ) as of 2008 [update] . [ 2 ]  Costs in Europe mostly ranged £4,000–£9,000 as of 2009 [update] . [ 3 ]


In the first 70 years of the 20th century, facelifts were performed by pulling on the skin on the face and cutting the loose parts off. The first facelift was reportedly performed by  Eugen Holländer  in 1901 in  Berlin . [ 4 ]  An elderly Polish female aristocrat asked him to:  "lift her cheeks and corners of the mouth". After much debate, he finally proceeded to excise an elliptical piece of skin around the ears. The first textbook about facial cosmetic surgery (1907) was written by  Charles Miller  (Chicago) entitled  The Correction of Featural Imperfections . [ 5 ]


In the First World War (1914–1918), the Dutch surgeon  Johannes Esser  made one of the most famous discoveries in the field of plastic surgery to date, namely the " skin graft inlay technique ," [ 6 ]  the technique was soon used on both English and German sides in the war. At the same time, the British plastic surgeon  Harold Delfs Gillies  used the Esser-graft to school all those who flocked towards him who wanted to study under him. That's how he earned the name "Father of 20th Century Plastic Surgery". In 1919, Dr Passot was known to publish one of the first papers on face-lifting, this consisted mainly of the elevating and redraping of the facial skin. After this, many others began to write papers on face-lifting in the 1920s. From then, the esthetic surgery was being performed on a large scale, form the basis of the reconstructive surgery. The first female plastic surgeon,  Suzanne Noël , played a large role in its development and she wrote one of the first books about esthetic surgery named  Chirurgie Esthetique, son rôle social . [ citation needed ]


In 1968,  Tord Skoog  introduced the concept of subfacial dissection, therefore providing suspension of the stronger deeper layer rather than relying on skin tension to achieve his facelift (he publishes his technique in 1974, with subfacial dissection of the  platysma  without detaching the skin in a posterior direction). [ 7 ]  In 1976, Mitz and Peyronie described the anatomical Superficial Musculoaponeurotic System, or SMAS, [ 8 ]  a term coined by  Paul Tessier , Mitz and Peyronie's tutor in  craniofacial surgery , after he had become familiar with Skoog's technique. After Skoog died of a heart attack, the  superficial muscular aponeurotic system  (SMAS) concept rapidly emerged to become the standard face-lifting technique, which was the first innovative change in facelift surgery in over 50 years. [ 9 ]


Tessier, who had his background in the craniofacial surgery, made the step to a  subperiosteal   dissection  via a coronal incision. [ 10 ]  In 1979, Tessier demonstrated that the subperiosteal undermining of the superior and lateral orbital rims allowed the elevation of the soft tissue and eyebrows with better results than the classic face-lifting. The objective was to elevate the soft tissue over the underlying skeleton to re-establish the patient's youthful appearance. [ citation needed ]


At the start of this period in the history of the facelift, there was a change in conceptual thinking, surgeons started to care more about minimizing scars, restoring the  subcutaneous  volume that was lost during the ageing process and they started making use of a  cranial  direction of the "lift" instead of posterior. [ citation needed ]


The technique for performing a facelift went from simply pulling on the skin and sewing it back to aggressive SMAS and deep plane surgeries to a more refined facelift where variable options are considered to have an aesthetically good and a more long-lasting effect. [ citation needed ]


A facelift is performed to  rejuvenate  the appearance of the face. Aging of the face is most shown by a change in position of the deep anatomical structures, notably the  platysma muscle , cheek fat and the  orbicularis oculi muscle . [ 11 ]   These lead up to three landmarks namely, an appearance of the jowl (a broken jaw line by  ptosis  of the platysma muscle), increased redundancy of the  nasolabial fold  (caused by a descent of cheek fat) and the increased distance from the ciliary margin to the inferior-most point of the orbicularis oculi muscle (caused by decreasing tone of the orbicularis oculi muscle). [ 11 ]   The skin is a fourth component in the aging of the face. The ideal age for face-lifting is at age 50 or younger, as measured by patient satisfaction. [ 12 ] [ 13 ] [ 14 ]  Some areas, such as the nasolabial folds or  marionette lines , in some cases can be treated more suitably with  Botox  or  liposculpture . [ citation needed ]


Contraindications to facelift surgery include severe  concomitant  medical problems, both physical and psychological. While not absolute contraindications, the risk of postoperative complications is increased in cigarette smokers and patients with hypertension and diabetes. [ 15 ]  These strong relative contraindications consist primarily of diseases predisposing to poor wound healing. Patients are typically asked to abstain from taking aspirin or other blood thinners for at least one week prior to surgery. Patients motivations and expectations are an important factor in order to determine the patient's medical status. A psychiatric illness leading to unreasonable expectations for the surgical outcome, such as a distorted perception of reality, can be a contraindication to surgery. Some kinds of  hypersensitivity  to  anesthesia  are a contraindication. [ citation needed ]


Many different procedures are used for rhytidectomy. [ 20 ]  The differences are mostly the type of incision, the invasiveness and the area of the face that is treated. Each surgeon practices multiple different types of facelift surgery. At a consultation the procedure with the best outcome is chosen for every patient. Expectations of the patient, the age, possible recovery time and areas to improve are some of the many factors taken in consideration before choosing a technique of rhytidectomy. [ citation needed ]


In the traditional facelift, an incision is made in front of the ear extending up into the hairline. The incision curves around the bottom of the ear and then behind it, usually ending near the hairline on the back of the neck. After the skin incision is made, the skin is separated from the deeper tissues with a scalpel or scissors (also called undermining) over the cheeks and neck. At this point, the deeper tissues (SMAS, the fascial suspension system of the face) can be tightened with sutures, with or without removing some of the excess deeper tissues. The skin is then redraped, and the amount of excess skin to be removed is determined by the surgeon's judgement and experience. The excess skin is then removed, and the skin incisions are closed with  sutures  and  staples .


The SMAS (Superficial Musculo Aponeurotic System) layer consists of suspensory ligaments that encase the cheek fat, thereby causing them to remain in their normal position. This procedure is often performed in tandem with blepharoplasty as an ancillary procedure. [ 21 ] [ 22 ]  Resuspension and securing the SMAS anatomical layer can lead to rejuvenation of the face, by counteracting aging and gravity caused  laxity . [ 22 ]  Modifications to this technique led to development of the "Composite Facelift" and "Deep plane Facelift." [ 23 ]


In order to correct the deepening of the nasolabial fold more accurately, the deep plane facelift was developed. Differing from the SMAS lift by freeing cheek fat and some muscles from their bone implement. This technique has a higher risk at damaging the facial nerve. The SMAS lift is an effective procedure to reposition the platysma muscle; however, the nasolabial fold is according to some surgeons better addressed by a deep plane facelift or composite facelift.


As well as in the deep plane facelift, in the composite facelift a deeper layer of tissue is mobilised and repositioned. The difference between these operating techniques is the extra repositioning and fixation of the orbicularis oculi muscle in the composite facelift procedure. The malar crescent caused by the orbicularis oculi ptosis can be addressed in a composite facelift. [ citation needed ]


The mid face area, the area between the cheeks, flattens and makes a woman's face look slightly more masculine. The mid face-lift is suggested to people where these changes occur, yet without a significant degree of  jowling  or sagging of the neck. In these cases a mid face-lift is sufficient to rejuvenate the face opposed to a full facelift, which is a more drastic surgery.
The ideal candidates for a mid face-lift is when a person is in his 40s, or if the cheeks appear to be sagging and the nasolabial area has laxity or skin folds.
To achieve a younger appearance the surgeon makes several small incisions along the hairline and inside the mouth, this way the fatty tissue layers can be lifted and repositioned. This way there are practically no scars. The fatty layer that lies over the cheekbones is also lifted and repositioned. This improves the nose-to-mouth lines and the roundness over the cheekbones. The recovery time is rather short and this procedure is often combined with a blepharoplasty (eyelid surgery)


The mini-facelift is the least invasive type of facelift which is similar to a full facelift, the only difference is the omission of the  neck lift  in the mini lift procedure. It is also called the ‘S’ lift because of the shape of the incision that is used or the ‘short-scar’ facelift. This lift is a more temporary solution to the ageing of the face which also has less downtime and is done on people who have deep nasolabial folds, sagging facial structures, yet still have a firm and well-contoured neck. The position of the incision is usually made from the hairline around the ear with scars hidden in the natural crease of the skin. The mini lift can be performed with an  endoscope , which is used to reposition the soft tissues. After this, the skin is repositioned by the surgeon with small sutures. [ 24 ]  This type of lift is a good alternative to the full facelift to people with premature ageing. [ citation needed ]


The subperiosteal facelift technique is done by vertically lifting the soft tissues of the face, completely separating it from the underlying facial bones and elevating it to a more esthetically pleasing position, correcting deep nasolabial folds and sagging cheeks. The technique is often combined with standard techniques, which provide a long-lasting rejuvenation of the face and is done in all age groups. The difference between this and other lifts is that the subperiosteal facelift has a longer period of facial swelling after the procedure. [ citation needed ]


With the skin-only facelift only the skin of the face is lifted and not the underlying SMAS, muscles or other structures. As the elastin fibers disintegrate, the skin itself loses elasticity in older patients. A skin only face lift requires skill in understanding the extent of safe removal of skin and the Vector of pull to get an optimal result. It can be done with a simple ellipse of skin removed with minimal undermining of skin flaps or more extensively with large skin flaps. It can last 5 to 10 years but some patients may want a touch-up at  6 to 12 months after the procedure. The reason that this option is considered is that it has fewer complications and quicker recovery. One of the father's of plastic surgery Sir Harold Gilles described a simple ellipse of skin excision in a socialite who was pleased with her quick recovery and outcome. Can be done for a simple jowl lift in a 35 to 45-year-old patient. [ citation needed ]


A technique called thread lift or non-surgical face lift simplifies the operation. Silicone threads with barbs are used to pull the face and neck skin upwards without the need of skin excision. These are non-absorbable threads and combination of these threads with other methods of facial rejuvenation reveals even better results. [ 25 ]  One such procedure is thread-lift with anti- ptosis  (APTOS) sutures. [ 26 ]


In the UK aesthetic practitioners—who administer thread lifts and other treatments—are not required to have any mandatory qualifications, although some treatments can cause serious complications. In  Liverpool  the  BBC  found 26 cosmetic training academies offering courses ranging in price from £150 to £5,000 in 2021, lasting from a couple of hours  online  to a couple of days of face-to-face training. A professionally trained cosmetic doctor, Vincent Wong, said that a thread lift is the most dangerous procedure an aesthetic practitioner can do. A great many things can go wrong, more so than any injectable treatment, because threads stay in the skin and cannot be pulled out; while the results can be very good, the procedure can also cause irreversible damage. The professional training of Wong—already a physician with a degree in surgery—in this procedure involved four courses over three months. [ 27 ]


A nurse sent undercover by the BBC to take and secretly film a course teaching thread lifting was shocked at the unprofessionalism and unsafe practices she was taught. While exceptional sterility is required to avoid possible long-term infection, there was no attempt to control infection. The tutor touched various objects and then the patient's face, and the procedure was carried out on a chair instead of a clean bed. Several blood vessels were accidentally punctured, and the patient was clearly in severe pain. Patients drank alcohol before the treatment and  vaped  during it. Ashton Collins, the director of Save Face,  a national register of accredited medical practitioners that provide non-surgical cosmetic treatments, said that "there's no doubt that if people following that course go on to do treatments [it] will cause a lot of complications". [ 27 ] [ 26 ]


The term MACS-lift – or Minimal Access Cranial Suspension lift – allows for the correction of sagging facial features through a short, minimal incision, elevating them vertically by suspending them from above. There are many advantages to having a MACS facelift versus a traditional facelift. For starters, the MACS-lift uses a shorter scar that is in front of the ear, instead of behind, which is much easier to hide. Overall, the MACS-lift surgery is safer because less skin is raised. This means that there is less risk of bleeding and nerve damage. The operation also takes less time, lasting 2.5 hours instead of the 3.5 hours that the traditional facelift requires. There is also a shorter recovery period, 2–3 weeks instead of 3–4 weeks. Finally, the results of the MACS-lift are very natural while the traditional facelift will often result in a "windswept" look. The MACS lift has been successfully used for to correct complication after thread-lift with APTOS. [ 26 ]


The most common complication is bleeding which usually requires a return to the operating room. Less common, but potentially serious, complications may include damage to the facial nerves and necrosis of the skin flaps or  infection . Although the facial plastic surgeon attempts to prevent and minimise the risk of complications, a rhytidectomy can have complications. As a risk to every operation, complications can be derived as a reaction to the anesthetics.


Hematoma  is the most seen complication after rhytidectomy. [ 17 ] [ 18 ] [ 28 ] [ 29 ] [ 30 ] [ 31 ] [ 32 ]  Arterial bleeding can cause the most dangerous hematomas, as they can lead to  dyspnea . Almost all of the hematomas occur within the first 24 hours after the rhytidectomy. [ 17 ] [ 18 ] [ 28 ]


Nerve injury  can be sustained during rhytidectomy. This kind of injury can be temporary or permanent and harm can be done to either  sensory  or  motor  nerves of the face. As a sensory nerve, the  great auricular nerve  is the most common nerve to get injured at a facelift procedure. [ 18 ] [ 28 ]  The most injured motor nerve is the facial nerve. [ 18 ] [ 33 ]


Skin necrosis can occur after a facelift operation.  Smoking  increases the risk of skin necrosis 12-fold. [ 15 ]  Scarring is considered a complication of facelift surgery.  Hypertrophic  scars can appear. A facelift requires skin incisions; however, the incisions in front of and behind the ear are usually inconspicuous.


Hair loss  in the portions of the incision within the hair-bearing scalp can rarely occur. A distortion of the hairline—and facial hair in men—can result after a rhytidectomy. There is a high incidence of  alopecia  after rhytidectomy. [ 34 ] [ 35 ]  The permanent hair loss is mostly seen at the incision site in the temporal areas. In men, the sideburns can be pulled backwards and upwards, resulting in an unnatural appearance if appropriate techniques are not employed to address this issue. Achieving a natural appearance following surgery in men can be more challenging due to their hair-bearing preauricular skin.
In both men and women, one of the signs of having had a facelift can be an earlobe which is pulled forwards and/or distorted. If too much skin is removed, or a more vertical vector not employed, the face can assume a pulled-back, "windswept" appearance. This appearance can also be due to changes in bone structure that generally happen with age.[2]


One of the most often overlooked (or not discussed) areas of a traditional facelift procedure is the effects on the anatomical positioning and angles of the ears. Most patients are, in many cases, not made aware that the vector forces in a facelift will lower the ears as well as change the angle of the ears. Ear lowering can be as much as 1 cm and change in the angle as much as 10 degrees.


Infection is a rare complication for patients who have undergone a rhytidectomy. [ 36 ]  Staphylococcus is the most usual causative organism for an infection after facelift surgery. [ 17 ]


The  salivatory nuclei  are two  general visceral efferent   nuclei  located in the caudal  pons , dorsal and lateral to the  facial nucleus . Their neurons give rise to  preganglionic   parasympathetic  nerve fibers in the control of  salivation . [ 1 ] [ 2 ]  The superior salivatory nucleus supplies fibers to the  intermediate nerve  (part of the  facial nerve  (CN VII). The inferior salivatory nucleus supplies fibers to the  glossopharyngeal nerve  (CN IX). [ 2 ]  The nuclei may also be involved in parasympathetic control of (extracranial and intracranial) head vasculature. [ 3 ]


The  superior salivatory nucleus  (or  nucleus salivatorius superior ) is a visceral motor  cranial nerve nucleus  of the  facial nerve (CN VII) . It is located in the  pontine tegmentum . [ citation needed ]  It projects  pre-ganglionic  visceral motor parasympathetic efferents (via  CN VII ) to the  pterygopalatine ganglion , and  submandibular ganglion . [ 4 ]


The term "lacrimal nucleus" is sometimes used to refer to a portion of the superior salivatory nucleus. [ 5 ]


Preganglionic  fibers en route to the pterygopalatine ganglion (destined to ultimately innervate the lacrimal gland and the mucosal glands of the nose, palate, and pharynx) subsequently form the  greater petrosal nerve , whereas those en route to the submandibular ganglion (destined to ultimately innervate the  submandibular  and  sublingual   salivary glands ) subsequently form the  chorda tympani . [ citation needed ]


The nucleus receives cortical stimuli from the  nucleus of solitary tract  via the  dorsal longitudinal fasciculus  and reflex connections. [ 4 ]


The  inferior salivatory nucleus  (or  nucleus salivatorius inferior ) is a cluster of  neurons  in the  medulla . It is the  general visceral efferent  (GVE) component of the  glossopharyngeal nerve  supplying the  parasympathetic  input to the  parotid gland  for  salivation .


It lies immediately caudal to the  superior salivatory nucleus  and just above the upper end of the  dorsal nucleus of the vagus nerve  in the medulla.


The preganglionic  parasympathetic  fibres originate in the inferior salivatory nucleus of the  glossopharyngeal nerve . They leave the glossopharyngeal nerve by its  tympanic  branch and then pass via the  tympanic plexus  and the  lesser petrosal nerve  to the  otic ganglion . Here, the fibres synapse, and the postganglionic fibers pass by communicating branches to the  auriculotemporal nerve , which conveys them to the  parotid gland . They produce vasodilator and secretomotor effects.


Parasympathetic input from fibers of the inferior salivatory nucleus stimulates the parotid gland to produce  vasodilation  and secrete  saliva .


The  semicircular canals  are three  semicircular  interconnected tubes located in the innermost part of each  ear , the  inner ear . The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the  bony labyrinth , a  periosteum -lined cavity on the  petrous part  of the  temporal bone  filled with  perilymph .


Each semicircular canal contains its respective  semicircular duct , i.e. the lateral, anterior and posterior semicircular ducts, which provide the  sensation  of  angular acceleration  and are part of the  membranous labyrinth —therefore filled with  endolymph .


The semicircular canals are a component of the  bony labyrinth  that are at right angles from each other and contain their respective semicircular duct. At one end of each of the semicircular ducts is a dilated sac called a  membranous ampulla , which is more than twice the diameter of the ducts. Each ampulla contains an ampullary crest, the  crista ampullaris  which consists of a thick gelatinous cap called a  cupula  and many  hair cells . The superior and posterior semicircular ducts are oriented vertically at right angles to each other. The lateral semicircular duct is about a 30-degree angle from the horizontal plane. The orientations of the ducts cause a different duct to be stimulated by movement of the head in different planes, and more than one duct is stimulated at once if the movement is off those planes. The lateral semicircular duct detects angular acceleration of the head when the head is turned and the anterior and posterior semicircular ducts detect vertical head movements when the head is moved up or down. [ 1 ]  When the head changes position, the  endolymph  in the ducts lags behind due to inertia and this acts on the cupula which bends the cilia of the hair cells. The stimulation of the hair cells sends the message to the brain that acceleration is taking place. The semicircular canals open into the vestibule by five orifices, one of the apertures being common to two of them.


Among species of mammals, the size of the semicircular canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their body size than those that move more cautiously. [ 2 ]


The  lateral semicircular canal  (also known as  horizontal  or  external semicircular canal ) is the shortest of the three canals. Movement of fluid within its duct corresponds to rotation of the head around a vertical axis (i.e. the neck), or in other words, rotation in the  transverse plane . This occurs, for example, when one turns the head from side to side (yaw axis).


It measures from 12 to 15 mm (0.47 to 0.59 in), and its arch is directed horizontally backward and laterally; thus each semicircular canal stands at right angles to the other two. Its ampullated end corresponds to the upper and lateral angle of the  vestibule , just above the  oval window , where it opens close to the ampullated end of the anterior semicircular canal; its opposite end opens at the upper and back part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other.


The  anterior semicircular canal  (also known as  superior semicircular canal ) contains the part of the  vestibular system  that detects rotations of the head in around the lateral axis, that is, rotation in the  sagittal plane . This occurs, for example, when nodding one's head (pitch axis).


It is 15 to 20 mm (0.59 to 0.79 in) in length, is vertical in direction, and is placed transversely to the long axis of the  petrous part  of the  temporal bone , on the anterior surface of which its arch forms a round projection. It describes about two-thirds of a circle. Its lateral extremity is ampullated, and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior semicircular canal to form the  crus osseum commune , which opens into the upper and medial part of the vestibule.


The  posterior semicircular canal  contains the part of the vestibular system that detects rotation of the head around the antero-posterior (sagittal) axis, or in other words, rotation in the  coronal plane . This occurs, for example, when one moves the head to touch the shoulders, or when doing a  cartwheel  (roll axis).


It is directed superiorly and posteriorly, as per its nomenclature, nearly parallel to the posterior surface of the petrous part of the temporal bone. The  vestibular aqueduct  is immediately medial to it. The posterior semicircular canal is part of the bony labyrinth and its duct is used by the vestibular system to detect rotations of the head in the coronal plane. It is the longest of the three semicircular canals, measuring from 18 to 22 mm (0.71 to 0.87 in). Its lower or ampullated end opens into the lower and back part of the vestibule, its upper into the  crus osseum commune .


Findings from a 2009 study demonstrated a critical late role for  bone morphogenetic protein 2  (BMP-2) in the morphogenesis of semicircular canals in the  zebrafish  inner ear. It is suspected that the role of BMP-2 in semicircular canal duct outgrowth is likely to be conserved between different  vertebrate  species. [ 3 ]


Additionally, it has been found that the two semicircular canals found in the  lamprey  inner ear are developmentally similar to the superior and posterior canals found in humans, as the canals of both organisms arise from two depressions in the  otic vesicle  during early development. These depressions first form in lampreys between the 11 and 42 millimeter larval stages and form in zebrafish 57 hours post-fertilization   [ 4 ]


The semicircular ducts provide sensory input for experiences of rotary movements. They are oriented along the  pitch, roll, and yaw axes . The lateral semicircular canal is oriented in the yaw axis, the anterior semicircular canal is oriented in the pitch axis, and the posterior semicircular canal is oriented in the roll axis.


Each duct is filled with a fluid called  endolymph  and contains motion sensors within the fluids. The base of each duct is enlarged, opening into the  utricle , and has a dilated sac at one end called the membranous ampulla. Within the ampulla is a mound of hair cells and supporting cells called  crista ampullaris . These hair cells have many cytoplasmic projections on the apical surface called  stereocilia  which are embedded in a gelatinous structure called the  cupula . As the head rotates, the duct moves, but the endolymph lags behind owing to  inertia . This deflects the cupula and bends the stereocilia within. The bending of these stereocilia alters an electric signal that is transmitted to the brain. Within approximately 10 seconds of achieving constant motion, the endolymph catches up with the movement of the duct and the cupula is no longer affected, stopping the sensation of acceleration. [ 1 ]  The specific gravity of the cupula is comparable to that of the surrounding endolymph. Consequently, the cupula is not displaced by gravity, unlike the  otolithic membranes  of the utricle and  saccule . As with macular hair cells, hair cells of the crista ampullaris will depolarise when the stereocilia deflect towards the  kinocilium . Deflection in the opposite direction results in hyperpolarisation and inhibition. In the lateral semicircular duct, ampullopetal flow is necessary for hair-cell stimulation, whereas ampullofugal flow is necessary for the anterior and posterior semicircular ducts. [ 5 ]


This adjustment period is in part the cause of an illusion known as " the leans " often experienced by pilots. As a pilot enters a turn, hair cells in the semicircular ducts are stimulated, telling the brain that the aircraft, and the pilot, are no longer moving in a straight line but rather making a banked turn. If the pilot were to sustain a constant rate turn, the endolymph would eventually catch up with the ducts and cease to deflect the cupula. The pilot would no longer feel as if the aircraft was in a turn. As the pilot exits the turn, the semicircular ducts are stimulated to make the pilot think that they are now turning in the opposite direction rather than flying straight and level. In response to this, the pilot will often lean in the direction of the original turn in an attempt to compensate for this illusion. A more serious form of this is called a  graveyard spiral . Rather than the pilot leaning in the direction of the original turn, they may actually re-enter the turn. As the endolymph stabilizes, the semicircular ducts stop registering the gradual turn and the aircraft slowly loses altitude until impact with the ground.  [ 6 ]


Jean Pierre Flourens , by destroying the horizontal semicircular canal of  pigeons , noted that they continue to fly in a circle, showing the purpose of the semicircular canals. [ 7 ]


This article incorporates text in the  public domain  from  page 1049  of the 20th edition of   Gray's Anatomy   (1918)


The  sense of smell , or  olfaction , [ nb 1 ]  is the  special sense  through which smells (or  odors ) are perceived. [ 2 ]  The sense of smell has many functions, including detecting desirable foods, hazards, and  pheromones , and plays a role in  taste .


In humans, it occurs when an  odor  binds to a  receptor  within the  nasal cavity , transmitting a signal through the  olfactory system . [ 3 ]   Glomeruli  aggregate signals from these receptors and transmit them to the  olfactory bulb , where the sensory input will start to interact with parts of the brain responsible for smell identification,  memory , and  emotion . [ 4 ]


There are many different things which can interfere with a normal sense of smell, including damage to the  nose  or smell receptors,  anosmia ,  upper respiratory infections ,  traumatic brain injury , and  neurodegenerative disease . [ 5 ] [ 6 ]


Early scientific study of the sense of smell includes the extensive doctoral dissertation of  Eleanor Gamble , published in 1898, which compared olfactory to other  stimulus modalities , and implied that smell had a lower intensity discrimination. [ 7 ]


As the Epicurean and atomistic Roman philosopher  Lucretius  (1st   century BCE) speculated, different odors are attributed to different shapes and sizes of "atoms" (odor molecules in the modern understanding) that stimulate the olfactory organ. [ 8 ]


A modern demonstration of that theory was the cloning of olfactory receptor proteins by  Linda B. Buck  and  Richard Axel  (who were awarded the  Nobel Prize  in 2004), and subsequent pairing of odor molecules to specific receptor proteins. [ 9 ]  Each odor receptor molecule recognizes only a particular molecular feature or class of odor molecules.  Mammals  have about a thousand  genes  that code for  odor reception . [ 10 ]  Of the genes that code for odor receptors, only a portion are functional. Humans have far fewer active odor receptor genes than other primates and other mammals. [ 11 ]  In mammals, each  olfactory receptor neuron  expresses only one functional odor receptor. [ 12 ]  Odor receptor nerve cells function like a key–lock system: if the airborne molecules of a certain chemical can fit into the lock, the nerve cell will respond.


There are, at present, a number of competing theories regarding the mechanism of odor coding and perception. According to the  shape theory , each receptor detects a feature of the odor  molecule . The weak-shape theory, known as the  odotope theory , suggests that different receptors detect only small pieces of molecules, and these minimal inputs are combined to form a larger olfactory perception (similar to the way visual perception is built up of smaller, information-poor sensations, combined and refined to create a detailed overall perception). [ 13 ]


According to a new study, researchers have found that a functional relationship exists between molecular volume of odorants and the olfactory neural response. [ 14 ]  An alternative theory, the  vibration theory  proposed by  Luca Turin , [ 15 ] [ 16 ]  posits that odor receptors detect the frequencies of vibrations of odor molecules in the infrared range by  quantum tunnelling . However, the behavioral predictions of this theory have been called into question. [ 17 ]  There is no theory yet that explains olfactory perception completely.


Flavor perception is an aggregation of  auditory ,  taste ,  haptic , and smell sensory information. [ 18 ]   Retronasal smell  plays the biggest role in the sensation of flavor. During the process of  mastication , the tongue manipulates food to release odorants. These odorants enter the nasal cavity during exhalation. [ 19 ]  The smell of food has the sensation of being in the mouth because of co-activation of the motor cortex and olfactory epithelium during mastication. [ 18 ]


Smell,  taste , and  trigeminal  receptors (also called  chemesthesis ) together contribute to  flavor . The human  tongue  can distinguish only among five distinct qualities of taste, while the nose can distinguish among hundreds of substances, even in minute quantities. It is during  exhalation  that the smell's contribution to flavor occurs, in contrast to that of proper smell, which occurs during the  inhalation  phase of breathing. [ 19 ]  The olfactory system is the only human sense that bypasses the  thalamus  and connects directly to the  forebrain . [ 20 ]


Smell and  sound  information has been shown to converge in the olfactory tubercles of  rodents . [ 21 ]  This neural convergence is proposed to give rise to a perception termed  smound . [ 22 ]  Whereas a  flavor  results from interactions between smell and taste, a smound may result from interactions between smell and sound.


The  MHC  genes (known as  HLA  in humans) are a group of genes present in many animals and important for the  immune system ; in general, offspring from parents with differing MHC genes have a stronger immune system. Fish, mice, and female humans are able to smell some aspect of the MHC genes of potential sex partners and prefer partners with MHC genes different from their own. [ 23 ] [ 24 ]  However, some research suggests that taking  hormonal contraception  can alter women's preference for partners with dissimilar MHC genes, thus resulting in a greater likelihood to choose partners with relatively similar MHC genes to their own. [ 25 ] [ 26 ]  Sexual orientation can also influence preference for different body odors, and some studies suggest that preference may be influenced by the putative pheromones  AND  and  EST . [ 27 ]


Humans can detect blood relatives from olfaction. [ 28 ]  Mothers can identify by body odor their biological children but not their stepchildren. Pre-adolescent children can olfactorily detect their full siblings but not half-siblings or step siblings, and this might explain  incest avoidance  and the  Westermarck effect . [ 29 ]  Functional imaging shows that this olfactory kinship detection process involves the frontal-temporal junction, the  insula , and the dorsomedial  prefrontal cortex , but not the primary or secondary olfactory cortices, or the related  piriform cortex  or  orbitofrontal cortex . [ 30 ]


Since  inbreeding  is detrimental, it tends to be avoided. In the house mouse, the  major urinary protein  (MUP) gene cluster provides a highly polymorphic scent signal of genetic identity that appears to underlie  kin recognition  and inbreeding avoidance. Thus, there are fewer matings between mice sharing MUP haplotypes than would be expected if there were random mating. [ 31 ]


Some animals use  scent trails  to guide movement, for example social insects may lay down a trail to a food source, or a  tracking dog  may follow the scent of its target. A number of  scent-tracking strategies  have been studied in different species, including gradient search or  chemotaxis , anemotaxis, klinotaxis, and tropotaxis. Their success is influenced by the  turbulence  of the air plume that is being followed. [ 32 ] [ 33 ]


Different people smell different odors, and most of these differences are caused by genetic differences. [ 34 ]  Although  odorant receptor  genes make up one of the largest gene families in the human genome, only a handful of genes have been linked conclusively to particular smells. For instance, the odorant receptor  OR5A1  and its genetic variants (alleles) are responsible for our ability (or failure) to smell β- ionone , a key aroma in foods and beverages. [ 35 ]  Similarly, the odorant receptor  OR2J3  is associated with the ability to detect the "grassy" odor, cis-3-hexen-1-ol. [ 36 ]  The preference (or dislike) of  cilantro  (coriander) has been linked to the olfactory receptor  OR6A2 . [ 37 ]


The importance and sensitivity of smell varies among different organisms; most  mammals  have a good sense of smell, whereas most  birds  do not, except the  tubenoses  (e.g.,  petrels  and  albatrosses ), certain species of new world  vultures , and the  kiwis . Also, birds have hundreds of olfactory receptors.  [ 38 ]  Although, recent analysis of the chemical composition of  volatile organic compounds  (VOCs) from  king penguin  feathers suggest that VOCs may provide olfactory cues, used by the penguins to locate their colony and recognize individuals. [ 39 ]  Among mammals, it is well developed in the  carnivores  and  ungulates , which must always be aware of each other, and in those that smell for their food, such as  moles . Having a strong sense of smell is referred to as  macrosmatic  in contrast to having a weak sense of smell which is referred to as  microsmotic .


Figures suggesting greater or lesser sensitivity in various species reflect experimental findings from the reactions of animals exposed to aromas in known extreme dilutions. These are, therefore, based on perceptions by these animals, rather than mere nasal function. That is, the brain's smell-recognizing centers must react to the stimulus detected for the animal to be said to show a response to the smell in question. It is estimated that dogs, in general, have an olfactory sense approximately ten thousand to a hundred thousand times more acute than a human's. [ 40 ]  This does not mean they are overwhelmed by smells our noses can detect; rather, it means they can discern a molecular presence when it is in much greater dilution in the carrier, air.


Scenthounds  as a group can smell one- to ten-million times more acutely than a human, and  bloodhounds , which have the keenest sense of smell of any dogs, [ 41 ]  have noses ten- to one-hundred-million times more sensitive than a human's. They were bred for the specific purpose of tracking humans, and can detect a  scent trail  a few days old. The second-most-sensitive nose is possessed by the  Basset Hound , which was bred to track and hunt rabbits and other small animals.


Grizzly bears  have a sense of smell seven times stronger than that of the bloodhound, essential for locating food underground. Using their elongated claws, bears dig deep trenches in search of burrowing animals and nests as well as roots, bulbs, and insects. Bears can detect the scent of food from up to eighteen miles away; because of their immense size, they often scavenge new kills, driving away the predators (including packs of wolves and human hunters) in the process.


The sense of smell is less developed in the  catarrhine   primates , and nonexistent in  cetaceans , which compensate with a well-developed sense of  taste . [ 41 ]  In some  strepsirrhines , such as the  red-bellied lemur , scent glands occur atop the head. In many species, smell is highly tuned to  pheromones ; a male  silkworm  moth, for example, can sense a single molecule of  bombykol .


Fish, too, have a well-developed sense of smell, even though they inhabit an aquatic environment. [ citation needed ]  Salmon utilize their sense of smell to identify and return to their home stream waters. Catfish use their sense of smell to identify other individual catfish and to maintain a social hierarchy. Many fishes use the sense of smell to identify mating partners or to alert to the presence of food.


Although conventional wisdom and lay literature, based on impressionistic findings in the 1920s, have long presented human smell as capable of distinguishing between roughly 10,000 unique odors, recent research has suggested that the average individual is capable of distinguishing over one trillion unique odors. [ 42 ]  Researchers in the most recent study, which tested the psychophysical responses to combinations of over 128 unique odor molecules with combinations composed of up to 30 different component molecules, noted that this estimate is "conservative" and that some subjects of their research might be capable of deciphering between a thousand trillion odorants, adding that their worst performer could probably still distinguish between 80   million scents. [ 43 ]  Authors of the study concluded, "This is far more than previous estimates of distinguishable olfactory stimuli. It demonstrates that the human olfactory system, with its hundreds of different olfactory receptors, far out performs the other senses in the number of physically different stimuli it can discriminate." [ 44 ]  However, it was also noted by the authors that the ability to distinguish between smells is not analogous to being able to consistently identify them, and that subjects were not typically capable of identifying individual odor stimulants from within the odors the researchers had prepared from multiple odor molecules. In November 2014 the study was strongly criticized by Caltech scientist Markus Meister, who wrote that the study's "extravagant claims are based on errors of mathematical logic." [ 45 ] [ 46 ]  The logic of his paper has in turn been criticized by the authors of the original paper. [ 47 ]


In humans and other  vertebrates , smells are sensed by  olfactory sensory neurons  in the  olfactory epithelium . The olfactory epithelium is made up of at least six morphologically and biochemically different cell types. [ 20 ]  The proportion of olfactory  epithelium  compared to respiratory epithelium (not innervated, or supplied with nerves) gives an indication of the animal's olfactory sensitivity. Humans have about 10 cm 2  (1.6 sq in) of olfactory epithelium, whereas some dogs have 170 cm 2  (26 sq in). A dog's olfactory epithelium is also considerably more densely innervated, with a hundred times more receptors per square centimeter. [ 48 ]  The sensory olfactory system integrates with other senses to form the perception of  flavor . [ 18 ]  Often, land organisms will have separate olfaction systems for smell and taste (orthonasal smell and  retronasal smell ), but water-dwelling organisms usually have only one system. [ 49 ]


Molecules of odorants passing through the  superior nasal concha  of the nasal passages dissolve in the  mucus  that lines the superior portion of the cavity and are detected by  olfactory receptors  on the  dendrites  of the olfactory sensory neurons. This may occur by diffusion or by the binding of the odorant to  odorant-binding proteins . The mucus overlying the epithelium contains  mucopolysaccharides , salts,  enzymes , and  antibodies  (these are highly important, as the olfactory neurons provide a direct passage for infection to pass to the  brain ). This mucus acts as a solvent for odor molecules, flows constantly, and is replaced approximately every ten minutes.


In  insects , smells are sensed by olfactory sensory neurons in the chemosensory  sensilla , which are present in insect antenna, palps, and tarsa, but also on other parts of the insect body. Odorants penetrate into the cuticle pores of chemosensory sensilla and get in contact with insect odorant-binding proteins (OBPs) or  Chemosensory proteins  (CSPs), before activating the sensory neurons.


The binding of the  ligand  (odor molecule or odorant) to the receptor leads to an  action potential  in the receptor neuron, via a  second messenger  pathway, depending on the organism. In mammals, the odorants stimulate  adenylate cyclase  to synthesize  cAMP  via a  G protein  called G olf . cAMP, which is the second messenger here, opens a  cyclic nucleotide-gated ion channel  (CNG), producing an influx of  cations  (largely  Ca 2+  with some  Na + ) into the cell, slightly depolarising it. The Ca 2+  in turn opens a Ca 2+ -activated  chloride channel , leading to efflux of  Cl − , further depolarizing the cell and triggering an action potential. Ca 2+  is then extruded through a  sodium-calcium exchanger . A calcium- calmodulin  complex also acts to inhibit the binding of cAMP to the cAMP-dependent channel, thus contributing to olfactory adaptation.


The main olfactory system of some mammals also contains small subpopulations of olfactory sensory neurons that detect and transduce odors somewhat differently. Olfactory sensory neurons that use trace amine-associated receptors (TAARs) to detect odors use the same second messenger signaling cascade as do the canonical olfactory sensory neurons. [ 50 ]  Other subpopulations, such as those that express the receptor guanylyl cyclase GC-D (Gucy2d) [ 51 ]  or the soluble guanylyl cyclase Gucy1b2, [ 52 ]  use a cGMP cascade to transduce their odorant ligands. [ 53 ] [ 54 ] [ 55 ]  These distinct subpopulations (olfactory subsystems) appear specialized for the detection of small groups of chemical stimuli.


This mechanism of transduction is somewhat unusual, in that cAMP works by directly binding to the  ion channel  rather than through activation of  protein kinase A . It is similar to the transduction mechanism for  photoreceptors , in which the second messenger  cGMP  works by directly binding to ion channels, suggesting that maybe one of these receptors was evolutionarily adapted into the other. There are also considerable similarities in the immediate processing of stimuli by  lateral inhibition .


Averaged activity of the receptor neurons can be measured in several ways. In vertebrates, responses to an odor can be measured by an  electro-olfactogram  or through calcium imaging of receptor neuron terminals in the olfactory bulb. In insects, one can perform  electroantennography  or calcium imaging within the olfactory bulb.


Olfactory sensory neurons project  axons  to the brain within the  olfactory nerve , ( cranial nerve   I). These nerve fibers, lacking  myelin  sheaths, pass to the  olfactory bulb  of the brain through perforations in the  cribriform plate , which in turn projects olfactory information to the  olfactory cortex  and other areas. [ 56 ]  The axons from the  olfactory receptors  converge in the outer layer of the olfactory bulb within small (≈50  micrometers  in diameter) structures called  glomeruli .  Mitral cells , located in the inner layer of the olfactory bulb, form synapses with the axons of the sensory neurons within glomeruli and send the information about the  odor  to other parts of the olfactory system, where multiple signals may be processed to form a synthesized olfactory perception. A large degree of convergence occurs, with 25,000 axons synapsing on 25 or so mitral cells, and with each of these mitral cells projecting to multiple glomeruli. Mitral cells also project to  periglomerular cells  and  granular cells  that inhibit the mitral cells surrounding it ( lateral inhibition ). Granular cells also mediate inhibition and excitation of mitral cells through pathways from centrifugal fibers and the anterior olfactory nuclei. Neuromodulators like  acetylcholine ,  serotonin  and  norepinephrine  all send axons to the olfactory bulb and have been implicated in gain modulation, [ 57 ]  pattern separation, [ 58 ]  and  memory  functions, [ 59 ]  respectively.


The mitral cells leave the olfactory bulb in the  lateral olfactory tract , which synapses on five major regions of the cerebrum: the  anterior olfactory nucleus , the  olfactory tubercle , the  amygdala , the  piriform cortex , and the  entorhinal cortex . The anterior olfactory nucleus projects, via the  anterior commissure , to the contralateral olfactory bulb, inhibiting it. The piriform cortex has two major divisions with anatomically distinct organizations and functions. The anterior piriform cortex (APC) appears to be better at determining the chemical structure of the odorant molecules, and the posterior piriform cortex (PPC) has a strong role in categorizing odors and assessing similarities between odors (e.g. minty, woody, and citrus are odors that can, despite being highly variant chemicals, be distinguished via the PPC in a concentration-independent manner). [ 60 ]  The piriform cortex projects to the  medial dorsal nucleus  of the thalamus, which then projects to the orbitofrontal cortex. The orbitofrontal cortex mediates conscious perception of the odor. [ citation needed ]  The three-layered piriform cortex projects to a number of thalamic and hypothalamic nuclei, the  hippocampus  and amygdala and the orbitofrontal cortex, but its function is largely unknown. The entorhinal cortex projects to the amygdala and is involved in emotional and autonomic responses to odor. It also projects to the hippocampus and is involved in motivation and memory. Odor information is stored in  long-term memory  and has strong connections to  emotional memory . This is possibly due to the olfactory system's close anatomical ties to the  limbic system  and hippocampus, areas of the brain that have long been known to be involved in emotion and place memory, respectively.


Since any one receptor is responsive to various odorants, and there is a great deal of convergence at the level of the olfactory bulb, it may seem strange that human beings are able to distinguish so many different odors. It seems that a highly complex form of processing must be occurring; however, as it can be shown that, while many neurons in the olfactory bulb (and even the pyriform cortex and amygdala) are responsive to many different odors, half the neurons in the orbitofrontal cortex are responsive to only one odor, and the rest to only a few. It has been shown through microelectrode studies that each individual odor gives a particular spatial map of excitation in the olfactory bulb. It is possible that the brain is able to distinguish specific odors through spatial encoding, but temporal coding must also be taken into account. Over time, the spatial maps change, even for one particular odor, and the brain must be able to process these details as well.


Inputs from the two  nostrils  have separate inputs to the brain, with the result that, when each nostril takes up a different odorant, a person may experience perceptual rivalry in the olfactory sense akin to that of  binocular rivalry . [ 61 ]


In  insects , smells are sensed by sensilla located on the antenna and maxillary palp and first processed by the  antennal lobe  (analogous to the  olfactory bulb ), and next by the  mushroom bodies  and  lateral horn .


The process by which olfactory information is coded in the brain to allow for proper perception is still being researched, and is not completely understood. When an odorant is detected by receptors, they in a sense break the odorant down, and then the brain puts the odorant back together for identification and perception. [ 62 ]  The odorant binds to receptors that recognize only a specific functional group, or feature, of the odorant, which is why the chemical nature of the odorant is important. [ 63 ]


After binding the odorant, the receptor is activated and will send a signal to the glomeruli  [ 63 ]  in the  olfactory bulb . Each glomerulus receives signals from multiple receptors that detect similar odorant features. Because several receptor types are activated due to the different chemical features of the odorant, several glomeruli are activated as well. The signals from the glomeruli are transformed to a pattern of oscillations of neural activities [ 64 ]  of the  mitral cells , the output neurons from the olfactory bulb. Olfactory bulb sends this pattern to the  olfactory cortex . Olfactory cortex is thought to have associative memories, [ 65 ]  so that it resonates to this bulbar pattern when the odor object is recognized. [ 66 ]  The cortex sends centrifugal feedback to the bulb. [ 67 ]  This feedback could suppress bulbar responses to the recognized odor objects, causing olfactory adaptation to background odors, so that the newly arrived foreground odor objects could be singled out for better recognition. [ 66 ] [ 68 ]  During odor search, feedback could also be used to enhance odor detection. [ 69 ] [ 66 ]  The distributed code allows the brain to detect specific odors in mixtures of many background odors. [ 70 ]


It is a general idea that the layout of brain structures corresponds to physical features of stimuli (called topographic coding), and similar analogies have been made in smell with concepts such as a layout corresponding to chemical features (called chemotopy) or perceptual features. [ 71 ]  While chemotopy remains a highly controversial concept, [ 72 ]  evidence exists for perceptual information implemented in the spatial dimensions of olfactory networks. [ 71 ]


Many animals, including most mammals and reptiles, but not humans, [ 73 ]  have two distinct and segregated olfactory systems: a main olfactory system, which detects volatile stimuli, and an accessory olfactory system, which detects fluid-phase stimuli. Behavioral evidence suggests that these fluid-phase stimuli often function as  pheromones , although pheromones can also be detected by the main olfactory system. In the accessory olfactory system, stimuli are detected by the  vomeronasal organ , located in the vomer, between the  nose  and the  mouth . Snakes use it to smell prey, sticking their tongue out and touching it to the organ. Some mammals make a facial expression called  flehmen  to direct stimuli to this organ.


The sensory receptors of the accessory olfactory system are located in the vomeronasal organ. As in the main olfactory system, the axons of these sensory neurons project from the vomeronasal organ to the  accessory olfactory bulb , which in the mouse is located on the dorsal-posterior portion of the main  olfactory bulb . Unlike in the main olfactory system, the axons that leave the accessory olfactory bulb do not project to the brain's cortex but rather to targets in the  amygdala  and  bed nucleus of the stria terminalis , and from there to the  hypothalamus , where they may influence aggression and mating behavior.


Insect olfaction refers to the function of  chemical receptors  that enable  insects  to detect and identify  volatile compounds  for  foraging , predator avoidance, finding  mating  partners (via  pheromones ) and locating  oviposition  habitats. [ 74 ]  Thus, it is the most important sensation for insects. [ 74 ]  Most important insect behaviors must be timed perfectly which is dependent on what they smell and when they smell it. [ 75 ]  For example, smell is essential for hunting in many species of  wasps , including  Polybia sericea .


The two organs insects primarily use for detecting odors are the  antennae  and specialized mouth parts called the maxillary palps. [ 76 ]  However, a recent study has demonstrated the olfactory role of ovipositor in fig wasps. [ 77 ]  Inside of these olfactory organs there are neurons called olfactory receptor neurons which, as the name implies, house receptors for scent molecules in their cell membranes. The majority of  olfactory receptor neurons  typically reside in the  antenna . These neurons can be very abundant, for example  Drosophila  flies have 2,600 olfactory sensory neurons. [ 76 ]


Insects are capable of smelling and differentiating between thousands of  volatile  compounds both  sensitively  and selectively. [ 74 ] [ 78 ]  Sensitivity is how attuned the insect is to very small amounts of an odorant or small changes in the concentration of an odorant. Selectivity refers to the insects' ability to tell one odorant apart from another. These compounds are commonly broken into three classes: short chain  carboxylic acids ,  aldehydes  and low molecular weight nitrogenous compounds. [ 78 ]  Some insects, such as the moth  Deilephila elpenor , use smell as a means to find food sources.


The tendrils of plants are especially sensitive to airborne  volatile organic compounds . Parasites such as  dodder  make use of this in locating their preferred hosts and locking on to them. [ 79 ]  The emission of volatile compounds is detected when foliage is browsed by animals. Threatened plants are then able to take defensive chemical measures, such as moving  tannin  compounds to their foliage.


Scientists have devised methods for quantifying the intensity of odors, in particular for the purpose of analyzing unpleasant or objectionable odors released by an industrial source into a community. Since the 1800s industrial countries have encountered incidents where proximity of an industrial source or landfill produced adverse reactions among nearby residents regarding airborne odor. The basic theory of odor analysis is to measure what extent of dilution with "pure" air is required before the sample in question is rendered indistinguishable from the "pure" or reference standard. Since each person perceives odor differently, an "odor panel" composed of several different people is assembled, each  sniffing  the same sample of diluted specimen air. A field  olfactometer  can be utilized to determine the magnitude of an odor.


Many air management districts in the  US  have numerical standards of acceptability for the intensity of odor that is allowed to cross into a residential property. For example, the  Bay Area Air Quality Management District  has applied its standard in regulating numerous industries, landfills, and sewage treatment plants. Example applications this district has engaged are the  San Mateo, California , wastewater treatment plant; the  Shoreline Amphitheatre  in  Mountain View, California ; and the  IT Corporation  waste ponds,  Martinez, California .


Systems of classifying odors include:


Specific terms are used to describe disorders associated with smelling:


Viruses can also infect the olfactory epithelium leading to a loss of the sense of olfaction. About 50% of patients with  SARS-CoV-2  (causing COVID-19) experience some type of  disorder associated with their sense of smell , including anosmia and parosmia.  SARS-CoV-1 ,  MERS-CoV  and even the flu ( influenza virus ) can also disrupt  olfaction . [ 86 ]


Media related to  Smell  at Wikimedia Commons


Septoplasty  ( Latin :  saeptum , "septum" +  Ancient Greek :  πλάσσειν ,  romanized :  plassein , "to shape"), or alternatively  submucous septal resection  and  septal reconstruction , [ 1 ]  is a corrective  surgical  procedure done to straighten a  deviated nasal septum  – the  nasal septum  being the partition between the two  nasal cavities . [ 2 ]  Ideally, the septum should run down the center of the  nose . When it deviates into one of the cavities, it narrows that cavity and impedes airflow. Deviated nasal septum or “crooked”  internal nose can occur at childbirth or as the result of an injury or other trauma. If the wall that functions as a separator of both sides of the nose is tilted towards one side at a degree greater than 50%, it might cause difficulty breathing. Often the inferior  turbinate  on the opposite side enlarges, which is termed  compensatory hypertrophy . Deviations of the septum can lead to nasal obstruction. Most surgeries are completed in 60 minutes or less, while the recovery time could be up to several weeks. Put simply, septoplasty is a surgery that helps repair the passageways in the nose making it easier to breathe. This surgery is usually performed on patients with a deviated septum, recurrent rhinitis, or sinus issues.


The procedure [ 3 ]  usually involves a judicious excision/realignment of a portion of the bone and/or cartilage in the nasal cavity. Under  general  or  local anesthesia , the surgeon works through the nostrils, making an incision in the lining of the septum to reach the cartilage/bone targeted in the operation. This may be performed using an endoscope or with open techniques. Sufficient cartilage and bone is preserved for structural support. After the septum is straightened, it may then be stabilized temporarily with small plastic tubes, splints, or sutures internally.  Skin grafts  can be placed internally to support the internal structures.


Apart from in patients with deviated nasal septum causing airway obstruction leading to difficulty with breathing, recurrent rhinitis, or sinusitis, septoplasty is done as an approach to  hypophysectomy . [ citation needed ]  It is sometimes done as well to cure recurrent   nosebleed (epistaxis)  due to  septal spur .


Septoplasty should not be done in acute nasal or sinus infection. It should also be avoided if the person has untreated  diabetes , severe  hypertension  or  bleeding diathesis . [ 4 ]


Unless there are unusual complications, there is no swelling or discoloration of the external nose or face with septoplasty alone.   Packing  is rare with modern surgical techniques, but  splinting  the inside of the nose for a few days is common; the splints are not visible externally. Patients who have nasal splints should receive prophylactic antibiotics against gram positive organisms to prevent possible toxic shock syndrome. One percent of patients can experience excessive bleeding afterwards — the risk period lasts up to two weeks. This could require packing or  cautery , but is generally handled safely and without compromise of the ultimate surgical result.  Septal perforation and septal hematoma are possible, as is a decrease in the sense of smell. [ 5 ]  Temporary numbness of the front upper teeth after surgery is common. [ 5 ]  Sometimes the numbness extends to the upper jaw and the tip of the nose.  This almost always resolves within several months.


The nasal tissues should mostly stabilize within 3-6 months post-surgery, although shifting is still possible for up to and over a year afterwards. [ 6 ]


A randomised controlled trial found that people who had septoplasty had a greater improvement in their symptoms and quality of life after 6 months than people who managed their nasal airway obstruction with nasal sprays. [ 7 ] [ 8 ]


A  sialogogue  (also spelled  sialagogue ,  ptysmagogue  or  ptyalagogue ) is a  substance , especially a  medication , that increases the flow rate of  saliva . [ 1 ]  The definition focuses on substances that promote  production or secretion of saliva  (proximal causation) rather than any food that is  mouthwatering  (distal causation that triggers proximal causation).


Sialogogues can be used in the treatment of  xerostomia  (the subjective feeling of having a dry mouth), to stimulate any functioning  salivary gland  tissue to produce more saliva. Saliva has a bactericidal effect, so when low levels of it are secreted, the risk of  caries  increases. [ 2 ]  Not only this, but fungal infections such as oral  candidosis  also can be a consequence of low salivary flow rates. The  buffer  effect of saliva is also important, neutralising acids that cause tooth enamel demineralisation.


The following are used in dentistry to treat xerostomia: [ 3 ]


A tincture is prepared from the root of the pyrethrium ( pyrethrum ) or pellitory (a number of plants in the  Chrysanthemum  family). It is found growing in Levant and parts of Limerick and Clare in  Ireland . The root powder was used as flavouring in tooth powders in the past. [ 5 ]


The inner surface of the  mastoid portion  of the  temporal bone  presents a deep, curved groove, the  sigmoid sulcus , which lodges part of the  transverse sinus ; in it may be seen the opening of the  mastoid foramen .


Sleep apnea  ( sleep apnoea  or  sleep apnœa  in  British English ) is a sleep-related breathing disorder in which repetitive  pauses in breathing , periods of shallow breathing, or collapse of the upper airway during  sleep  results in poor ventilation and sleep disruption. [ 10 ] [ 11 ]  Each pause in breathing can last for a few seconds to a few minutes and often occurs many times a night. [ 1 ]  A choking or snorting sound may occur as breathing resumes. [ 1 ]  Common symptoms include daytime sleepiness, snoring, and non restorative sleep despite adequate sleep time. [ 12 ]   Because the disorder disrupts normal sleep, those affected may experience sleepiness or feel tired during the day. [ 1 ]  It is often a chronic condition. [ 13 ]


Sleep apnea may be categorized as  obstructive sleep apnea  (OSA), in which breathing is interrupted by a blockage of air flow,  central sleep apnea  (CSA), in which regular unconscious breath simply stops, or a combination of the two. [ 1 ]  OSA is the most common form. [ 1 ]  OSA has four key contributors; these include a narrow, crowded, or collapsible upper airway, an ineffective pharyngeal dilator muscle function during sleep, airway narrowing during sleep, and unstable control of breathing (high loop gain). [ 14 ] [ 15 ]  In CSA, the basic neurological controls for breathing rate malfunction and fail to give the signal to inhale, causing the individual to miss one or more cycles of breathing. If the pause in breathing is long enough, the percentage of oxygen in the circulation can drop to a lower than normal level ( hypoxemia ) and the concentration of carbon dioxide can build to a higher than normal level ( hypercapnia ). [ 16 ]  In turn, these conditions of  hypoxia  and hypercapnia will trigger  additional  effects on the body such as  Cheyne-Stokes Respiration . [ 17 ]


Some people with sleep apnea are unaware they have the condition. [ 1 ]  In many cases it is first observed by a family member. [ 1 ]  An in-lab sleep study overnight is the preferred method for diagnosing sleep apnea. [ 15 ]  In the case of OSA, the outcome that determines disease severity and guides the treatment plan is the apnea-hypopnea index (AHI). [ 15 ]  This measurement is calculated from totaling all pauses in breathing and periods of shallow breathing lasting greater than 10 seconds and dividing the sum by total hours of recorded sleep. [ 10 ] [ 15 ]  In contrast, for CSA the degree of respiratory effort, measured by esophageal pressure or displacement of the thoracic or abdominal cavity, is an important distinguishing factor between OSA and CSA. [ 18 ]


A systemic disorder, sleep apnea is associated with a wide array of effects, including increased risk of  car accidents ,  hypertension ,  cardiovascular disease ,  myocardial infarction ,  stroke ,  atrial fibrillation ,  insulin resistance , higher incidence of  cancer , and  neurodegeneration . [ 19 ]  Further research is being conducted on the potential of using biomarkers to understand which chronic diseases are associated with sleep apnea on an individual basis. [ 19 ]


Treatment may include lifestyle changes, mouthpieces, breathing devices, and surgery. [ 1 ]  Effective lifestyle changes may include avoiding  alcohol , losing weight,  smoking  cessation, and sleeping on one's side. [ 20 ]  Breathing devices include the use of a  CPAP machine . [ 21 ]  With proper use, CPAP improves outcomes. [ 22 ]  Evidence suggests that CPAP may improve sensitivity to insulin, blood pressure, and sleepiness. [ 23 ] [ 24 ] [ 25 ]  Long term compliance, however, is an issue with more than half of people not appropriately using the device. [ 22 ] [ 26 ]  In 2017, only 15% of potential patients in developed countries used CPAP machines, while in developing countries well under 1% of potential patients used CPAP. [ 27 ] [ unreliable source? ]  Without treatment, sleep apnea may increase the risk of  heart attack ,  stroke ,  diabetes ,  heart failure ,  irregular heartbeat ,  obesity , and  motor vehicle collisions . [ 1 ]


OSA is a common sleep disorder. A large analysis in 2019 of the estimated prevalence of OSA found that OSA affects 936 million—1 billion people between the ages of 30–69 globally, or roughly every 1 in 10 people, and up to 30% of the elderly. [ 28 ]  Sleep apnea is somewhat more common in men than women, roughly a 2:1 ratio of men to women, and in general more people are likely to have it with older age and obesity. Other risk factors include being overweight, [ 19 ]  a family history of the condition, allergies, and enlarged  tonsils . [ 6 ]


The typical screening process for sleep apnea involves asking patients about common symptoms such as snoring, witnessed pauses in breathing during sleep and  excessive daytime sleepiness . [ 19 ]  There is a wide range in presenting symptoms in patients with sleep apnea, from being asymptomatic to falling asleep while driving. [ 19 ]   Due to this wide range in clinical presentation, some people are not aware that they have sleep apnea and are either misdiagnosed or ignore the symptoms altogether. [ 29 ]  A current area requiring further study involves identifying different subtypes of sleep apnea based on patients who tend to present with different clusters or groupings of particular symptoms. [ 19 ]


OSA may increase risk for driving accidents and work-related accidents due to sleep fragmentation from repeated arousals during sleep. [ 19 ]  If OSA is not treated it results in excessive daytime sleepiness and oxidative stress from the repeated drops in oxygen saturation, people are at increased risk of other systemic health problems, such as diabetes, hypertension or cardiovascular disease. [ 19 ]  Subtle manifestations of sleep apnea may include treatment refractory hypertension and cardiac arrhythmias and over time as the disease progresses, more obvious symptoms may become apparent. [ 12 ]  Due to the disruption in daytime cognitive state, behavioral effects may be present. These can include moodiness, belligerence, as well as a decrease in attentiveness and energy. [ 30 ]  These effects may become intractable, leading to depression. [ 31 ]


Obstructive sleep apnea can affect people regardless of sex, race, or age. [ 32 ]  However, risk factors include: [ 33 ]


Central sleep apnea is more often associated with any of the following risk factors: [ 18 ]


Obstructive sleep apnea