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.

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.

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.

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.

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.

The differential of hyposalivation significantly overlaps with that of xerostomia. A reduction in saliva production to about 50% of the normal unstimulated level will usually result in the sensation of dry mouth. Altered saliva composition may also be responsible for xerostomia.

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.

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.

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).

Burning mouth syndrome (BMS) is a burning sensation in the mouth with no underlying dental or medical cause. No related signs of disease are found in the mouth. People with burning mouth syndrome may also have a dry mouth sensation where no cause can be found such as reduced salivary flow, tingling in the mouth, or an altered taste or smell.

A burning sensation in the mouth can be a symptom of another disease when local or systemic factors are found to be implicated, and this is not considered to be burning mouth syndrome, which is a syndrome of medically unexplained symptoms. The International Association for the Study of Pain defines burning mouth syndrome as "a distinctive nosological entity characterized by unremitting oral burning or similar pain in the absence of detectable mucosal changes", and "burning pain in the tongue or other oral mucous membranes", and the International Headache Society defines it as "an intra-oral burning sensation for which no medical or dental cause can be found".

Due to insufficient evidence it is unclear if effective treatments exist.

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.

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.

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.

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

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.

The first signs of poisoning suggest an allergic reaction with the following symptoms:

- facial flushing/sweating

- burning-peppery taste sensations in the mouth and throat

- dizziness

- nausea

- headache

- tachycardia

- cold-like symptoms

It is caused by bacteria which if untreated can lead to many other problems in the body. Strep throat is most common in childhood but can affect people of all ages. It may present with throat pain, difficulty swallowing, painful and swollen tonsils, fever, headache, skin rash and flu. The diagnosis of strep throat is straight forward and the treatment requires a course of penicillin. However, if the treatment is not adequate, rheumatic fever can occur with resultant damage to the heart valves.

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.

The above symptoms can advance to:

- facial rash (intense itching may accompany the rash.)

- torso or body rash: The rash associated with scombroid poisoning is a form of urticaria, but most commonly does not include wheals (patchy areas of skin-swelling also known as hives) that may be seen in true allergies.

- edema (this is generalized if it occurs at all)

- short-term diarrhea

- abdominal cramps

Ramsay Hunt syndrome type 2, also known as herpes zoster oticus, is a disorder that is caused by the reactivation of varicella zoster virus in the geniculate ganglion, a nerve cell bundle of the facial nerve.

Ramsay Hunt syndrome type 2 typically presents with inability to move many facial muscles, pain in the ear, taste loss on the front of the tongue, dry eyes and mouth, and a vesicular rash..

During the summer months, allergies are a common cause of throat irritation. Many individuals have allergies to pet dander, dust, mites, pollen and molds that can trigger an allergic reaction which present with runny nose, red eyes, congested nose and throat irritation. Often a dry cough may also be present.

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.

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.

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.

Cancer patients undergoing chemotherapy usually become symptomatic four to five days after beginning treatment, reaching a peak at around day 10, and then slowly improving over the course of a few weeks. Mucositis associated with radiotherapy usually appears at the end of the second week of treatment and may last for six to eight weeks.

As a result of cell death in reaction to chemo- or radio-therapy, the mucosal lining of the mouth becomes thin, may slough off and then become red, inflamed and ulcerated. The ulcers may become covered by a yellowish white fibrin clot called a pseudomembrane. Peripheral erythema is usually present. Ulcers may range from 0.5 cm to greater than 4 cm. Oral mucositis can be severely painful. The degree of pain is usually related to the extent of the tissue damage. Pain is often described as a burning sensation accompanied by reddening. Due to pain, the patient may experience trouble speaking, eating, or even opening the mouth.

Dysgeusia, or an alteration in taste perception, is common, especially for those who are receiving concomitant radiation therapy to the neck and mouth area. "Taste blindness", or an altered sense of taste, is a temporary condition that occurs because of effects on taste buds that are mostly located in the tongue. Sometimes, only partial recovery of taste occurs. Common complaints are of food tasting too sweet or too bitter or of a continuous metallic taste.