Certain diagnostic tools can also be used to help determine the extent of dysgeusia. Electrophysiological tests and simple reflex tests may be applied to identify abnormalities in the nerve-to-brainstem pathways. For example, the blink reflex may be used to evaluate the integrity of the trigeminal nerve–pontine brainstem–facial nerve pathway, which may play a role in gustatory function.

Structural imaging is routinely used to investigate lesions in the taste pathway. Magnetic resonance imaging allows direct visualization of the cranial nerves. Furthermore, it provides significant information about the type and cause of a lesion. Analysis of mucosal blood flow in the oral cavity in combination with the assessment of autonomous cardiovascular factors appears to be useful in the diagnosis of autonomic nervous system disorders in burning mouth syndrome and in patients with inborn disorders, both of which are associated with gustatory dysfunction. Cell cultures may also be used when fungal or bacterial infections are suspected.

In addition, the analysis of saliva should be performed, as it constitutes the environment of taste receptors, including transport of tastes to the receptor and protection of the taste receptor. Typical clinical investigations involve sialometry and sialochemistry. Studies have shown that electron micrographs of taste receptors obtained from saliva samples indicate pathological changes in the taste buds of patients with dysgeusia and other gustatory disorders.

In order to further classify the extent of dysgeusia and clinically measure the sense of taste, gustatory testing may be performed. Gustatory testing is performed either as a whole-mouth procedure or as a regional test. In both techniques, natural or electrical stimuli can be used. In regional testing, 20 to 50 µL of liquid stimulus is presented to the anterior and posterior tongue using a pipette, soaked filter-paper disks, or cotton swabs. In whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient is asked to swish the solution around in the mouth.

Threshold tests for sucrose (sweet), citric acid (sour), sodium chloride (salty), and quinine or caffeine (bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test." In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water. Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row.

Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour). Direct scaling cannot be used to determine if a taste stimulus is being perceived at abnormal levels. In this case, magnitude matching is used, in which a patient is asked to rate the intensities of taste stimuli and stimuli of another sensory system, such as the loudness of a tone, on a similar scale. For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones. Assuming normal hearing, the results of this cross-sensory test show the relative strength of the sense of taste in relation to the loudness of the auditory stimulus. Although many of the tests are based on ratings using the direct scaling method, some tests do use the magnitude-matching procedure.

Other tests include identification or discrimination of common taste substances. Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily. In addition to techniques based on the administration of chemicals to the tongue, electrogustometry is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical direct current. Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue. Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.

BMS is a diagnosis of exclusion, i.e. all other explanations for the symptoms are ruled out before the diagnosis is made. There are no clinically useful investigations that would help to support a diagnosis of BMS (by definition all tests would have normal results), but blood tests and / or urinalysis may be useful to rule out anemia, deficiency states, hypothyroidism and diabetes. Investigation of a dry mouth symptom may involve sialometry, which objectively determines if there is any reduction of the salivary flow rate (hyposalivation). Oral candidiasis can be tested for with use of a swabs, smears, an oral rinse or saliva samples. It has been suggested that allergy testing ("e.g.", patch test) is inappropriate in the absence of a clear history and clinical signs in people with a burning sensation in the mouth. The diagnosis of a people with a burning symptom may also involve psychologic screening e.g. depression questionnaires.

The second edition of the International Classification of Headache Disorders lists diagnostic criteria for "Glossodynia and Sore Mouth":

A diagnosis of hyposalivation is based predominantly on the clinical signs and symptoms. There is little correlation between symptoms and objective tests of salivary flow, such as sialometry. This test is simple and noninvasive, and involves measurement of all the saliva a patient can produce during a certain time, achieved by dribbling into a container. Sialometery can yield measures of stimulated salivary flow or unstimulated salivary flow. Stimulated salivary flow rate is calculated using a stimulant such as 10% citric acid dropped onto the tongue, and collection of all the saliva that flows from one of the parotid papillae over five or ten minutes. Unstimulated whole saliva flow rate more closely correlates with symptoms of xerostomia than stimulated salivary flow rate. Sialography involves introduction of radio-opaque dye such as iodine into the duct of a salivary gland. It may show blockage of a duct due to a calculus. Salivary scintiscanning using technetium is rarely used. Other medical imaging that may be involved in the investigation include chest x-ray (to exclude sarcoidosis), ultrasonography and magnetic resonance imaging (to exclude Sjögren's syndrome or neoplasia). A minor salivary gland biopsy, usually taken from the lip, may be carried out if there is a suspicion of organic disease of the salivary glands. Blood tests and urinalysis may be involved to exclude a number of possible causes. To investigate xerophthalmia, the Schirmer test of lacrimal flow may be indicated. Slit-lamp examination may also be carried out.

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.

Anosmia can be diagnosed by doctors by using acetylcysteine tests. Doctors will begin with a detailed elicitation of history. Then the doctor will ask for any related injuries in relation to anosmia which could include upper respiratory infections or head injury. Psychophysical Assessment of order and taste identification can be used to identify anosmia. A nervous system examination is performed to see if the cranial nerves are damaged. The diagnosis as well as the degree of impairment can now be tested much more efficiently and effectively than ever before thanks to "smell testing kits" that have been made available as well as screening tests which use materials that most clinics would readily have. Occasionally, after accidents, there is a change in a patient's sense of smell. Particular smells that were present before are no longer present. On occasion, after head traumas, there are patients who have unilateral anosmia. The sense of smell should be tested individually in each nostril.

Many cases of congenital anosmia remain unreported and undiagnosed. Since the disorder is present from birth the individual may have little or no understanding of the sense of smell, hence is unaware of the deficit. It may also lead to reduction of appetite.

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.

Local damage and inflammation that interferes with the taste buds or local nervous system such as that stemming from radiation therapy, glossitis, tobacco use, and denture use also cause ageusia. Other known causes include loss of taste sensitivity from aging (causing a difficulty detecting salty or bitter taste), anxiety disorder, cancer, renal failure and liver failure.

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

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.

When untreated, the prognosis for ORS is generally poor. It is chronic, lasting many years or even decades with worsening of symptoms rather than spontaneous remission. Transformation to another psychiatric condition is unlikely, although very rarely what appears to be ORS may later manifest into schizophrenia, psychosis, mania, or major depressive disorder. The most significant risk is suicide.

When treated, the prognosis is better. In one review, the proportion of treated ORS cases which reported various outcomes were assessed. On average, the patients were followed for 21 months (range: 2 weeks to 10 years). With treatment, 30% recovered (i.e. no longer experienced ORS odor beliefs and thoughts of reference), 37% improved and in 33% there was a deterioration in the condition (including suicide) or no change from the pre-treatment status.

The successful treatment of xerostomia is difficult to achieve and often unsatisfactory. This involves finding any correctable cause and removing it if possible, but in many cases it is not possible to correct the xerostomia itself, and treatment is symptomatic, and also focuses on preventing tooth decay through improving oral hygiene. Where the symptom is caused by hyposalivation secondary to underlying chronic disease, xerostomia can be considered permanent or even progressive. The management of salivary gland dysfunction may involve the use of saliva substitutes and/or saliva stimulants:

- Saliva substitutes – these include SalivaMAX, water, artificial salivas (mucin-based, carboxymethylcellulose-based), and other substances (milk, vegetable oil).

- Saliva stimulants – organic acids (ascorbic acid, malic acid), chewing gum, parasympathomimetic drugs (choline esters, e.g. pilocarpine hydrochloride, cholinesterase inhibitors), and other substances (sugar-free mints, nicotinamide).

Saliva substitutes can improve xerostomia, but tend not to improve the other problems associated with salivary gland dysfunction. Parasympathomimitic drugs (saliva stimulants) such as pilocarpine may improve xerostomia symptoms and other problems associated with salivary gland dysfunction, but the evidence for treatment of radiation-induced xerostomia is limited. Both stimulants and substitutes relieve symptoms to some extent. Salivary stimulants are probably only useful in people with some remaining detectable salivary function. A systematic review of the treatment of dry mouth found no strong evidence to suggest that a specific topical therapy is effective. The review reported limited evidence that oxygenated glycerol triester spray was more effective than electrolyte sprays. Sugar free chewing gum increases saliva production but there is no strong evidence that it improves symptoms. There is a suggestion that intraoral devices and integrated mouthcare systems may be effective in reducing symptoms, but there was a lack of strong evidence. A systematic review of the management of radiotherapy induced xerostomia with parasympathomimetic drugs found that there was limited evidence to support the use of pilocarpine in the treatment of radiation-induced salivary gland dysfunction. It was suggested that, barring any contraindications, a trial of the drug be offered in the above group (at a dose of five mg three times per day to minimize side effects). Improvements can take up to twelve weeks. However, pilocarpine is not always successful in improving xerostomia symptoms. The review also concluded that there was little evidence to support the use of other parasympathomimetics in this group.

A 2013 review looking at non-pharmacological interventions reported a lack of evidence to support the effects of electrostimulation devices, or acupuncture, on symptoms of dry mouth.

The frequency of phantosmia is rare in comparison with the frequency of parosmia. Parosmia has been estimated to be in 10-60% of patients with olfactory dysfunction and from studies, it has been shown that it can last anywhere from 3 months to 22 years. Smell and taste problems result in over 200,000 visits to physicians annually in the US. Lately, it has been thought that phantosmia might co-occur with Parkinson's disease. However, its potential to be a premotor biomarker for Parkinson's is still up for debate as not all patients with Parkinson's disease have olfactory disorders

The most challenging task for the examiner is to determine and obtain the correct symptoms and associate them with one of the olfactory disorders, as there are several of them and they are related to each other.

The first step the examiner usually takes is to investigate if the problem is olfactory or gustatory related. As it may be that the patient releases certain bodily odors that are causing them to have this perception.

If the examiner is able to confirm that the problem is olfactory related, the next step is to determine which olfactory disorder the patient suffers from. The following is a list of possible olfactory disorders:

- anosmia

- dysosmia

- hyperosmia

- hyposmia

- parosmia or troposmia

- phantosmia

The second step is very difficult for both the examiner and the patient as the patient has some difficulty describing their perception of the phantom odor. Furthermore, the patient is in a position of stress and anxiety thus it is crucial that the examiner be patient.

After determining the nature of the disorder, and confirming phantosmia, the examiner must then have the patient describe their perception of the phantom odor. In many cases, patients have described the odor to be that of something burning and rotten and have described it to be unpleasant and foul.

The third step for the examiner is to determine the health history of the patient to take note of head trauma, accidents, upper respiratory infections, allergic rhinitis or chronic rhinitis. Although these may be events that have resulted in the phantom odor, studies conducted by Zilstrof have found that the majority of phantosmia patients have no previous history of head trauma and upper respiratory infections.

Though anosmia caused by brain damage cannot be treated, anosmia caused by inflammatory changes in the mucosa may be treated with glucocorticoids. Reduction of inflammation through the use of oral glucocorticoids such as prednisone, followed by long term topical glucocorticoid nasal spray, would easily and safely treat the anosmia. A prednisone regimen is adjusted based on the degree of the thickness of mucosa, the discharge of oedema and the presence or absence of nasal polyps. However, the treatment is not permanent and may have to be repeated after a short while. Together with medication, pressure of the upper area of the nose must be mitigated through aeration and drainage.

Anosmia caused by a nasal polyp may be treated by steroidal treatment or removal of the polyp.

There have also been cases where the use of acupuncture have successfully treated anosmia.

Although very early in development, gene therapy has restored a sense of smell in mice with congenital anosmia when caused by ciliopathy. In this case a genetic condition had affected cilia in their bodies which normally enabled them to detect air-borne chemicals, and an adenovirus was used to implant a working version of the IFT88 gene into defective cells in the nose, which restored the cilia and allowed a sense of smell.

For a 52-year-old woman, phantosmia occurring as fluctuating episodes occurred for a period of 27 years, and there was no discernible reason for the onset of symptoms. She could weaken the symptoms by rinsing her nose with a saline solution, and by going to sleep. The smells she would encounter often were very unpleasant, resembling a burnt and rotten fruity odor. When her family doctor prescribed her the antidepressant venlafaxine, she noticed that the drug resulted in the complete elimination of her phantosmia symptoms. This discovery has caused scientists and doctors to research if a link between phantosmia and mild depressive disorders exists, and this idea is supported by the reported improvement of phantosmia after repeated transcranial stimulation used to treat depression.

Cases have been reported from many different countries around the world. It is difficult to estimate the prevalence of ORS in the general population because data are limited and unreliable, and due to the delusional nature of the condition and the characteristic secrecy and shame.

For unknown reasons, males appear to be affected twice as commonly as females. High proportions of ORS patients are unemployed, single, and not socially active. The average age reported is around 20–21 years, with almost 60% of cases occurring in subjects under 20 in one report, although another review reported an older average age for both males (29) and females (40).

A variety of surgeries have been performed including microvascular decompression (MVD) of the fifth, ninth, and tenth nerves; as well as partial cutting of the nervus intermedius, geniculate ganglion, chorda tympani and/or the ninth and tenth cranial nerves.

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.

Rumination syndrome is diagnosed based on a complete history of the individual. Costly and invasive studies such as gastroduodenal manometry and esophageal Ph testing are unnecessary and will often aid in misdiagnosis. Based on typical observed features, several criteria have been suggested for diagnosing rumination syndrome. The primary symptom, the regurgitation of recently ingested food, must be consistent, occurring for at least six weeks of the past twelve months. The regurgitation must begin within 30 minutes of the completion of a meal. Patients may either chew the regurgitated matter or expel it. The symptoms must stop within 90 minutes, or when the regurgitated matter becomes acidic. The symptoms must not be the result of a mechanical obstruction, and should not respond to the standard treatment for gastroesophageal reflux disease.

In adults, the diagnosis is supported by the absence of classical or structural diseases of the gastrointestinal system. Supportive criteria include a regurgitant that does not taste sour or acidic, is generally odourless, is effortless, or at most preceded by a belching sensation, that there is no retching preceding the regurgitation, and that the act is not associated with nausea or heartburn.

Patients visit an average of five physicians over 2.75 years before being correctly diagnosed with rumination syndrome.

Treatment with the steroid "prednisone" and the antiviral drug "acyclovir 800mg 5 times a day" is controversial, with some studies showing to achieve complete recovery in patients if started within the first three days of facial paralysis, with chances of recovery decreasing as treatment was delayed. Delay of treatment may result in permanent facial nerve paralysis. However, some studies demonstrate that even when steroids are started promptly, only 22% of all patient achieve full recovery of facial paralysis.

Treatment apparently has no effect on the recovery of hearing loss. Diazepam is sometimes used to treat the vertigo.

There is presently no known cure for rumination. Proton pump inhibitors and other medications have been used to little or no effect.

Treatment is different for infants and the mentally handicapped than for adults and adolescents of normal intelligence. For adults and adolescents,Biofeedback and relaxation techniques, to be practice after eating or whenever regurgitation occurs, has proven to be most effective.

Among infants and the mentally handicapped, behavioral and mild aversive training has been shown to cause improvement in most cases. Aversive training involves associating the ruminating behavior with negative results, and rewarding good behavior and eating. Placing a sour or bitter taste on the tongue when the individual begins the movements or breathing patterns typical of his or her ruminating behavior is the generally accepted method for aversive training,

although some older studies advocate the use of pinching.

In patients of normal intelligence, rumination is not an intentional behavior and is habitually reversed using diaphragmatic breathing to counter the urge to regurgitate. Alongside reassurance, explanation and habit reversal, patients are shown how to breathe using their diaphragms prior to and during the normal rumination period. A similar breathing pattern can be used to prevent normal vomiting. Breathing in this method works by physically preventing the abdominal contractions required to expel stomach contents.

Supportive therapy and diaphragmatic breathing has shown to cause improvement in 56% of cases, and total cessation of symptoms in an additional 30% in one study of 54 adolescent patients who were followed up 10 months after initial treatments. Patients who successfully use the technique often notice an immediate change in health for the better. Individuals who have had bulimia or who intentionally induced vomiting in the past have a reduced chance for improvement due to the reinforced behavior. The technique is not used with infants or young children due to the complex timing and concentration required for it to be successful. Most infants grow out of the disorder within a year or with aversive training.

Extreme deviation of nasal septum may be accompanied by atrophic rhinitis on the wider side.

Tube dependency is a new clinical phenomenon and isn't recognized as a separate diagnosis yet, thus there is no standardized valid diagnostic inventory to classify it. Tube dependency should be considered in any patient who remains tube-fed despite having the basic ability to ingest food orally and in absence of specific medical reasons to remain tube fed. In this case, assessment by a clinician experienced with eating development, tube management and tube weaning is recommended

There are two known methods that can aid in the possible diagnosis of tube dependency:

1. Observation of affected infants during a feeding situation by experienced clinicians.

2. A multiaxial diagnostic system focused on eating behavior disorders. It consists of five axis, which are compatible with the axis of the DSM-IV and subdivided in currently six feeding (eating behavior) disorders with different origins.

Clinicians will often follow a diagnostic checklist to test whether or not an individual is exhibiting behaviors and characteristics that may lead to a diagnosis of ARFID. Clinicians will look at the variety of foods an individual consumes, as well as the portion size of accepted foods. They will also question how long the avoidance or refusal of particular foods has lasted, and if there are any associated medical concerns, such as malnutrition. Unlike most eating disorders, there may be a higher rate of ARFID in young boys, than there is in young girls.