Both taste and smell disorders are diagnosed by an otolaryngologist, a doctor of the ear, nose, throat, head, and neck. An otolaryngologist can determine the extent of your taste disorder by measuring the lowest concentration of a taste quality that you can detect or recognize. You may also be asked to compare the tastes of different substances or to note how the intensity of a taste grows when a substance’s concentration is increased.

Scientists have developed taste testing in which the patient responds to different chemical concentrations. This may involve a simple “sip, spit, and rinse” test, or chemicals may be applied directly to specific areas of the tongue.

The alterations in the sense of taste, usually a metallic taste, and sometimes smell are the only symptoms. The duration of the symptoms of dysgeusia depends on the cause. If the alteration in the sense of taste is due to gum disease, dental plaque, a temporary medication, or a short-term condition such as a cold, the dysgeusia should disappear once the cause is removed. In some cases, if lesions are present in the taste pathway and nerves have been damaged, the dysgeusia may be permanent.

Ageusia ( ) is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning "pleasant/savory taste"). It is sometimes confused with anosmia – a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia – a partial loss of taste – and dysgeusia – a distortion or alteration of taste.

Dysgeusia, also known as parageusia, is a distortion of the sense of taste. Dysgeusia is also often associated with ageusia, which is the complete lack of taste, and hypogeusia, which is a decrease in taste sensitivity. An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary symptom. The distortion in the sense of taste is the only symptom, and diagnosis is usually complicated since the sense of taste is tied together with other sensory systems. Common causes of dysgeusia include chemotherapy, asthma treatment with albuterol, and zinc deficiency. Different drugs could also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms of dysgeusia. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.

By definition, BMS has no signs. Sometimes affected persons will attribute the symptoms to sores in the mouth, but these are in fact normal anatomic structures (e.g. lingual papillae, varices). Symptoms of BMS are variable, but the typical clinical picture is given below, considered according to the Socrates pain assessment method (see table). If clinical signs are visible, then another explanation for the burning sensation may be present. Erythema (redness) and edema (swelling) of papillae on the tip of the tongue may be a sign that the tongue is being habitually pressed against the teeth. The number and size of filiform papillae may be reduced. If the tongue is very red and smooth, then there is likely a local or systemic cause (e.g. eythematous candidiasis, anemia).

True hyposalivation may give the following signs and symptoms:

- Dental caries (xerostomia related caries) – Without the anticariogenic actions of saliva, tooth decay is a common feature and may progress much more aggressively than it would otherwise ("rampant caries"). It may affect tooth surfaces that are normally spared, e.g., cervical caries and root surface caries. This is often seen in patients who have had radiotherapy involving the major salivary glands, termed radiation-induced caries.

- Acid erosion. Saliva acts as a buffer and helps to prevent demineralization of teeth.

- Oral candidiasis – A loss of the antimicrobial actions of saliva may also lead to opportunistic infection with "Candida" species.

- Ascending (suppurative) sialadenitis – an infection of the major salivary glands (usually the parotid gland) that may be recurrent. It is associated with hyposalivation, as bacteria are able to enter the ductal system against the diminished flow of saliva. There may be swollen salivary glands even without acute infection, possibly caused by autoimmune involvement.

- Dysgeusia – altered taste sensation (e.g., a metallic taste) and dysosmia, altered sense of smell.

- Intraoral halitosis – possibly due to increased activity of halitogenic biofilm on the posterior dorsal tongue (although dysgeusia may cause a complaint of nongenuine halitosis in the absence of hyposalivation).

- Oral dysesthesia – a burning or tingling sensation in the mouth.

- Saliva that appears thick or ropey.

- Mucosa that appears dry.

- A lack of saliva pooling in the floor of the mouth during examination.

- Dysphagia – difficulty swallowing and chewing, especially when eating dry foods. Food may stick to the tissues during eating.

- The tongue may stick to the palate, causing a clicking noise during speech, or the lips may stick together.

- Gloves or a dental mirror may stick to the tissues.

- Fissured tongue with atrophy of the filiform papillae and a lobulated, erythematous appearance of the tongue.

- Saliva cannot be "milked" (expressed) from the parotid duct.

- Difficulty wearing dentures, e.g., when swallowing or speaking. There may be generalized mucosal soreness and ulceration of the areas covered by the denture.

- Mouth soreness and oral mucositis.

- Lipstick or food may stick to the teeth.

- A need to sip drinks frequently while talking or eating.

- Dry, sore, and cracked lips and angles of mouth.

- Thirst.

However, sometimes the clinical findings do not correlate with the symptoms experienced. E.g., a person with signs of hyposalivation may not complain of xerostomia. Conversely a person who reports experiencing xerostomia may not show signs of reduced salivary secretions (subjective xerostomia). In the latter scenario, there are often other oral symptoms suggestive of oral dysesthesia ("burning mouth syndrome"). Some symptoms outside the mouth may occur together with xerostomia.

These include:

- Xerophthalmia (dry eyes).

- Inability to cry.

- Blurred vision.

- Photophobia (light intolerance).

- Dryness of other mucosae, e.g., nasal, laryngeal, and/or genital.

- Burning sensation.

- Itching or grittiness.

- Dysphonia (voice changes).

There may also be other systemic signs and symptoms if there is an underlying cause such as Sjögren's syndrome, for example, joint pain due to associated rheumatoid arthritis.

A burning sensation in the mouth may be primary (i.e. burning mouth syndrome) or secondary to systemic or local factors. Other sources refer to a "secondary BMS" with a similar definition, i.e. a burning sensation which is caused by local or systemic factors, or "where oral burning is explained by a clinical abnormality". However this contradicts the accepted definition of BMS which specifies that no cause can be identified. "Secondary BMS" could therefore be considered a misnomer. BMS is an example of dysesthesia, or a distortion of sensation.

Some consider BMS to be a variant of atypical facial pain. More recently, BMS has been described as one of the 4 recognizable symptom complexes of chronic facial pain, along with atypical facial pain, temporomandibular joint dysfunction and atypical odontalgia. BMS has been subdivided into three general types, with type two being the most common and type three being the least common. Types one and two have unremitting symptoms, whereas type three may show remitting symptoms.

- Type 1 - Symptoms not present upon waking, and then increase throughout the day

- Type 2 - Symptoms upon waking and through the day

- Type 3 - No regular pattern of symptoms

Sometimes those terms specific to the tongue (e.g. "glossodynia") are reserved for when the burning sensation is located only on the tongue.

Xerostomia is the subjective feeling of oral dryness, which is often (but not always) associated with hypofunction of the salivary glands. The term is derived from the Greek words ξηρός ("xeros") meaning "dry" and στόμα ("stoma") meaning "mouth". A drug or substance that increases the rate of salivary flow is termed a sialogogue.

Hyposalivation is a clinical diagnosis that is made based on the history and examination, but reduced salivary flow rates have been given objective definitions. Salivary gland hypofunction has been defined as any objectively demonstrable reduction in whole and/or individual gland flow rates. An unstimulated whole saliva flow rate in a normal person is 0.3–0.4 ml per minute, and below 0.1 ml per minute is significantly abnormal. A stimulated saliva flow rate less than 0.5 ml per gland in 5 minutes or less than 1 ml per gland in 10 minutes is decreased. The term subjective xerostomia is sometimes used to describe the symptom in the absence of any detectable abnormality or cause. Xerostomia may also result from a change in composition of saliva (from serous to mucous). Salivary gland dysfunction is an umbrella term for the presence of either xerostomia or salivary gland hypofunction.

Hypogeusia is a reduced ability to taste things (to taste sweet, sour, bitter, or salty substances). The complete lack of taste is referred to as ageusia.

Causes of hypogeusia include the chemotherapy drug bleomycin, an antitumor antibiotic as well as zinc deficiency.

Geniculate ganglionitis or geniculate neuralgia (GN), also called nervus intermedius neuralgia, Ramsay Hunt syndrome, or Hunt's neuralgia, is a rare disorder characterized by severe paroxysmal neuralgic pain deep in the ear, that may spread to the ear canal, outer ear, mastoid or eye regions. GN may also occur in combination with trigeminal or glossopharyngeal neuralgia.

The pain of GN is sharp, shooting or burning and can last for hours. Painful attacks can be triggered by cold, noise, swallowing or touch, but triggers are usually unique to the sufferer. Other related symptoms that may be experienced include increased salivation, bitter taste, tinnitus and vertigo.

GN is rare, and only limited data is available regarding the incidence, prevalence, and risk factors associated with this condition. Middle-aged adults, however, seem to be predominantly affected, women more than men.

GN may be caused by compression of somatic sensory branch of cranial nerve VII which goes through the nervus intermedius. In sufferers of GN, signals sent along these nerves are altered and interpreted by the geniculate ganglion (a structure in the brain) as GN pain. GN may also develop following herpes zoster oticus (Ramsay Hunt syndrome), where cold sores occur on the ear drum or ear. This may also be associated with facial paresis (weakness), tinnitus, vertigo and deafness. Disorders of lacrimation, salivation and/or taste sometimes accompany the pain. There is a common association with herpes zoster.

Anosmia is the inability to perceive odor or a lack of functioning olfaction—the loss of the sense of smell. Anosmia may be temporary, but some forms such as from an accident, can be permanent. Anosmia is due to a number of factors, including an inflammation of the nasal mucosa, blockage of nasal passages or a destruction of one temporal lobe. Inflammation is due to chronic mucosa changes in the paranasal sinus lining and the middle and superior turbinates.

When anosmia is caused by inflammatory changes in the nasal passageways, it is treated simply by reducing inflammation. It can be caused by chronic meningitis and neurosyphilis that would increase intracranial pressure over a long period of time, and in some cases by ciliopathy including ciliopathy due to primary ciliary dyskinesia (Kartagener syndrome, Afzelius' syndrome or Siewert's syndrome).

Many patients may experience unilateral anosmia, often as a result of minor head trauma. This type of anosmia is normally only detected if both of the nostrils are tested separately. Using this method of testing each nostril separately will often show a reduced or even completely absent sense of smell in either one nostril or both, something which is often not revealed if both nostrils are simultaneously tested.

A related term, hyposmia, refers to a decreased ability to smell, while hyperosmia refers to an increased ability to smell. Some people may be anosmic for one particular odor. This is known as "specific anosmia". The absence of the sense of smell from birth is called congenital anosmia.

The onset of ORS may be sudden, where it usually follows after a precipitating event, or gradual.

Anosmia can have a number of harmful effects. Patients with sudden onset anosmia may find food less appetizing, though congenital anosmics rarely complain about this, and none report a loss in weight. Loss of smell can also be dangerous because it hinders the detection of gas leaks, fire, and spoiled food. The common view of anosmia as trivial can make it more difficult for a patient to receive the same types of medical aid as someone who has lost other senses, such as hearing or sight.

Losing an established and sentimental smell memory (e.g. the smell of grass, of the grandparents' attic, of a particular book, of loved ones, or of oneself) has been known to cause feelings of depression.

Loss of olfaction may lead to the loss of libido, though this usually does not apply to congenital anosmics.

Often people who have congenital anosmia report that they pretended to be able to smell as children because they thought that smelling was something that older/mature people could do, or did not understand the concept of smelling but did not want to appear different from others. When children get older, they often realize and report to their parents that they do not actually possess a sense of smell, often to the surprise of their parents.

A study done on patients suffering from anosmia found that when testing both nostrils, there was no anosmia revealed; however, when testing each nostril individually, tests showed that the sense of smell was usually affected in only one of the nostrils as opposed to both. This demonstrated that unilateral anosmia is not uncommon in anosmia patients.

The defining feature of ORS is excessive thoughts of having offensive body odor(s) which are detectable to others. The individual may report that the odor comes from: the nose and/or mouth, i.e. halitosis (bad breath), the anus, the genitals, the skin generally, or specifically the groin, armpits or feet. The source(s) of the supposed odor may also change over time. There are also some who are unsure of the exact origin of the odor. The odor is typically reported to be continuously present. The character of the odor may be reported as similar to bodily substances, e.g. feces, flatus, urine, sweat, vomitus, semen, vaginal secretions; or alternatively it may be an unnatural, non-human or chemical odor, e.g. ammonia, detergent, rotten onions, burnt rags, candles, garbage, burning fish, medicines, old cheese. Again, the reported character of the odor complaint may change over time. Halitosis appears to be the most common manifestation of ORS, with 75% complaining of bad breath, alone or in combination with other odors. The next most common complaint was sweat (60%).

Although all individuals with ORS believe they have an odor, in some cases the individual reports they cannot perceive the odor themselves. In the latter cases, the belief arises via misinterpretation of the behavior of others or with the rationale that a disorder of smell which prevents self detection of the odor (i.e. anosmia) exists. In the cases where the non-existent odor can be detected, this is usually considered as phantosmia (olfactory hallucination). Olfactory hallucination can be considered the result of the belief in an odor delusion, or the belief a result of the olfactory hallucination. In one review, the individual with ORS was unreservedly convinced that he or she could detect the odor themselves in 22% of cases, whilst in 19% there was occasional or intermittent detection and in 59% lack of self-detection was present.

Some distinguish "delusional" and "non-delusional" forms of ORS. In the delusional type, there is complete conviction that the odor is real. In the non-delusional type, the individual is capable of some insight into the condition, and can recognize that the odor might not be real, and that their level of concern is excessive. Others argue that reported cases of ORS present a spectrum of different levels of insight. Since sometimes the core belief of ORS is not of delusional intensity, it is argued that considering the condition as a form of delusional disorder, as seems to occur in the DSM, is inappropriate. In one review, in 57% of cases the beliefs were fixed, held with complete conviction, and the individual could not be reassured that the odor was non existent. In 43% of cases the individual held the beliefs with less than complete conviction, and was able to varying degrees to consider the possibility that the odor was not existent.

Other symptoms may be reported and are claimed to be related to the cause of the odor, such as malfunction of the anal sphincter, a skin disease, "diseased womb", stomach problems or other unknown organic disease. Excessive washing in ORS has been reported to cause the development of eczema.

Other olfactory disorders such as hyposmia and anosmia have been found to be a symptom of mood disorders (depression). However, it is not known what olfactory disorders occur and if they are indeed a symptom of a depressive disorder.

It has been found that phantosmia may be an early sign of the neurodegenerative disease Parkinson's disease. It may also be a sign of an intracranial hemorrhage (brain tumours or epilepsy).

Other studies have also found that the symptoms of phantosmia have been alleviated after the patient has been treated for depression.

Another case of a 70-year-old male reported that his first abnormal symptoms were irregular bowel movements. After this the patient developed irregular eye movements and had developed a sleep and behavior disorder after this he developed phantosmia; which was described to be as "stinky and unpleasant". The patient did not display the following symptoms: loss of awareness, confusion, automatisms, convulsive seizures, auditory/visual hallucinations.

The symptoms and signs include acute facial nerve paralysis, pain in the ear, taste loss in the front two-thirds of the tongue, dry mouth and eyes, and an erythematous vesicular rash in the ear canal, the tongue, and/or hard palate.

Since the vestibulocochlear nerve is in proximity to the geniculate ganglion, it may also be affected, and patients may also suffer from tinnitus, hearing loss, and vertigo. Involvement of the trigeminal nerve can cause numbness of the face.

Diagnostic criteria:

A. Pain paroxysms of intermittent occurrence, lasting for seconds or minutes, in the depth of the ear

B. Presence of a trigger area in the posterior wall of the auditory canal

C. Not attributed to another disorder

Phantosmia (phantom smell), also called an olfactory hallucination, is smelling an odor that is not actually there. It can occur in one nostril or both. Unpleasant phantosmia, cacosmia, is more common and is often described as smelling something that is burned, foul, spoiled, or rotten. Experiencing occasional phantom smells is normal and usually goes away on its own in time. When hallucinations of this type do not seem to go away or when they keep coming back, it can be very upsetting and can disrupt an individual's quality of life.

Olfactory hallucinations can be caused by common medical conditions such as nasal infections, nasal polyps, or dental problems. It can result from neurological conditions such as migraines, head injuries, strokes, Parkinson's disease, seizures, or brain tumors. It can also be a symptom of certain mental disorders such as depression, bipolar disorder, intoxication or withdrawal from drugs and alcohol, or psychotic disorders. Environmental exposures are sometimes the cause as well, such as smoking, exposure to certain types of chemicals (e.g., insecticides or solvents), or radiation treatment for head or neck cancer.

A physician can determine if the problem is with the sense of smell (olfactory system) or taste (gustatory system), or if it is caused by a neurological or psychiatric disorder. Phantosmia usually goes away on its own, though this can sometimes be gradual and occur over several years. When caused by an illness (e.g., sinusitis), it should go away when the illness resolves. If the problem persists or causes significant discomfort, a doctor might recommend nasal saline drops, antidepressant or anticonvulsant medications, anesthesia to parts of the nose, or in very rare circumstances, surgical procedures to remove the olfactory nerves or bulbs.

Flavor is perceived by the combination of the sense of taste, sense of smell, and the trigeminal nerve (CN V). The gustatory system is responsible for differentiation between sweet, sour, salty, bitter, and umami. The olfactory system recognizes the odorants as they pass to the olfactory epithelium via a retronasal pathway. This explains why we can identify a variety of flavors in spite of only having five types of taste receptors. The trigeminal nerve senses texture, pain, and temperature of food. For example, the cooling effect of menthol or the burning sensation of spicy food.

Diagnosing a patient can be difficult as they are often frustrated from ineffective therapy and being told they have mental illnesses. Some patients actually have trouble deciding whether they have a taste or smell problem. In this case asking questions about food choices will help determine whether a patient has a smell or taste disorder. It is important to identify whether the distortion applies to an inhaled odorant or if an odor exists without the stimulus. The distortion of an odorant is presented in two types: the stimuli are different from what one remembers and in the second, everything has a similar smell. A clinical history can also help determine what kind of disorder one has because events such as respiratory infection and head trauma are usually indications of parosmia where as phantosmias usually have no history of such events and occur spontaneously. Unfortunately there are no accurate diagnostic tests or methods for dysosmia. Evaluation must be done through questionnaires and medical history.

Ageusia is the loss of taste, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (meaning "pleasant/savory taste"). It is sometimes confused with anosmia (a loss of the sense of smell). Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami, most of what is perceived as the sense of taste is actually derived from smell. True ageusia is relatively rare compared to hypogeusia (a partial loss of taste) and dysgeusia (a distortion or alteration of taste).

Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the lingual nerve and the glossopharyngeal nerve. The lingual nerve passes taste for the front two-thirds of the tongue and the glossopharyngeal nerve passes taste for the back third of the tongue. The lingual nerve can also be damaged during otologic surgery, causing a feeling of metal taste.

Taste loss can vary from true aguesia, a complete loss of taste, to hypogeusia, a partial loss of taste, to dysgeusia, a distortion or alteration of taste. The primary cause of ageusia involves damage to the lingual nerve, which receives the stimuli from taste buds for the front two-thirds of the tongue, or the glossopharyngeal nerve, which acts similarly for the back third. Damage may be due to neurological disorders, such as Bell’s palsy or multiple sclerosis, as well as infectious diseases such as meningoencephalopathy. Other causes include a vitamin B deficiency, as well as taste bud death due to acidic/spicy foods, radiation, and/or tobacco use.

Rumination syndrome in adults is a complicated disorder whose symptoms can mimic those of several other gastroesophogeal disorders and diseases. Bulimia nervosa and gastroparesis are especially prevalent among the misdiagnoses of rumination.

Bulimia nervosa, among adults and especially adolescents, is by far the most common misdiagnosis patients will hear during their experiences with rumination syndrome. This is due to the similarities in symptoms to an outside observer—"vomiting" following food intake—which, in long-term patients, may include ingesting copious amounts to offset malnutrition, and a lack of willingness to expose their condition and its symptoms. While it has been suggested that there is a connection between rumination and bulimia, unlike bulimia, rumination is not self-inflicted. Adults and adolescents with rumination syndrome are generally well aware of their gradually increasing malnutrition, but are unable to control the reflex. In contrast, those with bulimia intentionally induce vomiting, and seldom re-swallow food.

Gastroparesis is another common misdiagnosis. Like rumination syndrome, patients with gastroparesis often bring up food following the ingestion of a meal. Unlike rumination, gastroparesis causes vomiting (in contrast to regurgitation) of food, which is not being digested further, from the stomach. This vomiting occurs several hours after a meal is ingested, preceded by nausea and retching, and has the bitter or sour taste typical of vomit.

Oral galvanism is a phenomenon that can occur when two or more dissimilar metals in dental restorations which are bathed in saliva, or a single metal in contact with two electrolytes such as saliva and pulp fluid tissue, produce an electric current. When associated with pain, the term galvanic pain has been used.

While there seems to be little dispute that the presence of dissimilar metals can cause an electric current and can, in some cases, cause a metallic taste in the mouth, some discomfort, and also possibly lead to premature corrosion of the metallic restorations, there is controversy over other claimed effects. Those other claimed effects include oral discomfort, skin irritation, and headaches . Many scientific studies dispute these claims.

This galvanism is said by some to be able to affect immune levels and the trigeminal nerve, causing a variety of other symptoms, such as insomnia, vertigo, and memory loss. The condition is claimed to be idiopathic, depending on the individual’s state of health, and to have varying effects on oral microbial communities. It was first proposed in 1878.

Oral galvanism is sometimes treated by replacing metallic amalgam restorations with ceramic or polymer restorations.

While the number and severity of symptoms varies among individuals, repetitive regurgitation of undigested food (known as rumination) after the start of a meal is always present. In some individuals, the regurgitation is small, occurring over a long period of time following ingestion, and can be rechewed and swallowed. In others, the amount can be bilious and short lasting, and must be expelled.

While some only experience symptoms following some meals, most experience episodes following any ingestion, from a single bite to a massive feast. However, some long-term patients will find a select couple of food or drink items that do not trigger a response.

Unlike typical vomiting, the regurgitation is typically described as effortless and unforced. There is seldom nausea preceding the expulsion, and the undigested food lacks the bitter taste and odour of stomach acid and bile.

Symptoms can begin to manifest at any point from the ingestion of the meal to 120 minutes thereafter. However, the more common range is between 30 seconds to 1 hour after the completion of a meal. Symptoms tend to cease when the ruminated contents become acidic.

Abdominal pain (38.1%), lack of fecal production or constipation (21.1%), nausea (17.0%), diarrhea (8.2%), bloating (4.1%), and dental decay (3.4%) are also described as common symptoms in day-to-day life. These symptoms are not necessarily prevalent during regurgitation episodes, and can happen at any time. Weight loss is often observed (42.2%) at an average loss of 9.6 kilograms, and is more common in cases where the disorder has gone undiagnosed for a longer period of time, though this may be expected of the nutrition deficiencies that often accompany the disorder as a consequence of its symptoms. Depression has also been linked with rumination syndrome, though its effects on rumination syndrome are unknown.

Acid erosion of the teeth can be a feature of rumination, as can halitosis (bad breath).

Similarly to vision loss, hearing loss can vary from full or partial inability to detect some or all frequencies of sound which can typically be heard by members of their species. For humans, this range is approximately 20 Hz to 20 kHz at ~6.5 dB, although a 10 dB correction is often allowed for the elderly. Primary causes of hearing loss due to an impaired sensory system include long-term exposure to environmental noise, which can damage the mechanoreceptors responsible for receiving sound vibrations, as well as multiple diseases, such as HIV or meningitis, which damage the cochlea and auditory nerve, respectively.

Hearing loss may be gradual or sudden. Hearing loss may be very mild, resulting in minor difficulties with conversation, or as severe as complete deafness. The speed with which hearing loss occurs may give clues as to the cause. If hearing loss is sudden, it may be from trauma or a problem with blood circulation. A gradual onset is suggestive of other causes such as aging or a tumor. If you also have other associated neurological problems, such as tinnitus or vertigo, it may indicate a problem with the nerves in the ear or brain. Hearing loss may be unilateral or bilateral. Unilateral hearing loss is most often associated with conductive causes, trauma, and acoustic neuromas. Pain in the ear is associated with ear infections, trauma, and obstruction in the canal.