Ageusia: Causes, Types, Treatment

Ageusia: Description

Ageusia is the term used by physicians to describe a failure of taste perception. This extremely rare form of taste disorder (dysgeusia) can be divided into three subtypes:

  • Complete ageusia: This is understood to be the complete loss of the ability to taste, i.e. those affected can no longer taste anything at all.
  • functional ageusia: The ability to taste is very clearly limited.
  • partial ageusia: Affected persons can no longer perceive certain tastes (e.g. sweet).

Overall, taste disorders are rarer than olfactory disorders. However, they can be extremely unpleasant and distressing for those affected. After all, a normal sense of taste is necessary to enjoy food.

This is how taste develops

  • Taste buds: They are the “sense organ” for taste. A human being has several thousand taste buds in the area of the tongue and palate. They enable us to distinguish between five different tastes: sweet, sour, bitter, salty and umami (Japanese for savory-spicy).
  • specific cranial nerves: Of the total of twelve cranial nerves, three are responsible for taste (VII, X and IX). These three nerve pathways conduct the information from the taste buds to the brain.
  • Brain: In the brain, the information coming from the taste buds converges, is processed and thus only perceived as taste.

What other forms of taste disorder are there?

Hypogeusia

decreased sensitivity to taste compared to young, healthy subjects

Hypergeusia

hypersensitive sense of taste compared to young, healthy subjects

Parageusia

altered perception of taste sensations (e.g. sweet can be perceived as bitter)

Phantogeusia

Perception of taste sensations without stimulus source (e.g., inexplicable metallic taste in the mouth). Also called “tasting hallucination.”

Ageusia: Causes and possible diseases

Ageusia can be epithelial, nervous and/or central. This means that the taste perception of the affected person is disturbed in at least one of the three stations of taste perception (taste buds in the oral mucosa – cranial nerves – brain). The possible causes for this are manifold. They include, for example:

  • Infections such as flu-like infection (cold), flu, sinusitis, covid-19 or oral mucosa infections with bacteria or fungus
  • Sjögren’s syndrome and other causes of dry mouth
  • psychiatric diseases such as depression
  • diabetes mellitus
  • hypothyroidism
  • liver and kidney diseases
  • inflammation of the brain (encephalitis) or cranial nerves (neuritis)
  • Brain tumors
  • Traumatic brain injury
  • Epilepsy
  • multiple sclerosis
  • Diseases associated with the death of brain cells (neurodegenerative diseases), e.g. Alzheimer’s disease
  • Medications, e.g., antidepressants, chlorhexidine (e.g., as a mouth rinse for inflammation of the oral mucosa or gums), terbinafine (medication for fungal infections), cytostatics (medications for chemotherapy)
  • Radiation therapy in the head and neck area, e.g., for cancer of the larynx
  • Operations, e.g. ear surgery or removal of the palatal tonsils (tonsillectomy)
  • contact with toxic substances (incl. nicotine and alcohol)
  • poor oral hygiene

Sometimes no cause can be found for a tasting disorder. It is then called idiopathic.

Ageusia: When should you see a doctor?

If the sensation of taste is absent (ageusia) or otherwise altered (hypogeusia, parageusia, etc.), this can be an indication of a previously undetected health disorder. Both rather harmless causes and dangerous diseases are possible as the cause of the taste disorder.

Anyone who suspects that he or she has a taste disorder should not hesitate, but go to the family doctor. He or she will be able to assess whether further clarification by specialists is necessary.

Ageusia: What does the doctor do?

The first point of contact for a taste disorder (such as ageusia) is the family doctor. He or she can make an initial assessment by taking the patient’s medical history in a detailed interview (anamnesis) and by performing physical and laboratory examinations.

If necessary, he will refer the patient to a specialist – a specialist in ear, nose and throat medicine. Depending on the (suspected) cause of the ageusia, other specialists may also be consulted, for example a neurologist (nerve specialist) or radiologist (x-ray specialist).

Medical history (anamnesis)

At the beginning of the visit to the doctor, there is a detailed discussion between the patient and the doctor, which can provide important information about the cause of the taste disorder. Your doctor will ask you various questions. For example:

  • Do you no longer taste anything at all (ageusia) or is the sensation of taste altered in some other way?
  • How long have you had the taste disorder?
  • Did the taste disorder come on suddenly or did it come on gradually?
  • Is the taste disorder always present or only intermittent?
  • Do you have problems with smelling in addition to the taste disorder?
  • Are you taking any medications? If yes, which ones?
  • Do you smoke? Do you drink alcohol? How much in each case and since when?
  • Do you have any pre-existing conditions (for example, diabetes mellitus, autoimmune diseases)?
  • Have you suffered a head injury in the past?
  • Have you been/are you being treated with radiation or chemotherapy for cancer?
  • Apart from taste disorders, do you have any other symptoms such as dizziness, visual disturbances, headaches or sensory disturbances in your arms or legs?

Physical examination

In the next step, the doctor thoroughly examines the mouth, nose and throat. This can detect many obvious causes of ageusia, such as inflammation. In addition, the doctor palpates the lymph nodes in the head and neck area. If they are swollen, this may indicate an inflammatory disease, among other things.

Because the cause of ageusia is sometimes in the cranial nerves or brain, the doctor will also perform an orienting neurological examination: Simple tests are used to determine if there may be any cranial nerve or brain function deficits.

Taste tests

Within the framework of classical gustometry, test solutions of different tastes (sweet, sour, etc.) can be administered one after the other – for example, as drops on the tongue or as a spray solution in the mouth – to screen the general (global) taste function (in the whole mouth). The patient should try to identify them correctly.

It is also possible to test different dilutions (concentrations) of each solution of a flavor. This not only helps to determine whether the patient can identify different tastes, but also to determine, based on the dilution, how good the taste sensation is for the specific taste (intensity estimation).

Another way to test regional tasting ability is electrogustometry. This involves applying a very low current to the surface of the tongue. It irritates the taste buds (like a flavoring agent) and thus normally triggers a sour or metallic taste perception in the patient. The taste threshold is then determined separately for each half of the tongue – i.e., the lowest stimulus (in the form of the lowest current intensity) that evokes a taste perception in the patient.

Further tests

In addition to these specific tests of the sense of taste, other examinations are often necessary to identify a cause for ageusia (or other taste disorder). These include, but are not limited to:

  • Blood tests, e.g., if a vitamin, zinc, or iron deficiency, undetected diabetes, liver disease, or an infection is suspected (looking for specific antibodies to the pathogens)
  • Measurement of saliva production
  • fine tissue (histopathological) examination of biopsies (tissue samples) of the tongue and oral mucosa
  • dental examination

Therapies

In the case of a taste disorder such as ageusia, treatment depends on the underlying cause. Patience is usually required from the patient. The tasting system has an exceptionally high ability to recover spontaneously after damage. However, unless the cause of the taste disorder is a simple cold or similarly temporary and harmless, recovery can take a long time (usually months or even years).

Here are some example causative therapy options for ageusia:

  • In the case of iron or vitamin deficiency, the physician may prescribe appropriate supplements to compensate. In the case of hypothyroidism, replacement preparations are also necessary – i.e. hormone preparations that compensate for the lack of thyroid hormones.
  • If medications are the cause of ageusia, the attending physician may suggest discontinuing the preparation – if possible – or switching to another preparation.
  • If a medication has caused a zinc deficiency, which in turn causes a taste disorder, a zinc preparation is useful. In other cases of taste disorders, zinc intake is sometimes recommended as well, although the effectiveness here is not always proven.
  • If a tumor disease is the trigger of a taste disorder such as ageusia, conservative treatment with medication, radiation or surgery may be indicated.
  • Other underlying diseases associated with ageusia or another taste disorder (such as diabetes, multiple sclerosis, etc.) must also be treated professionally.

Ageusia: What you can do yourself

Some people with functional ageusia still have a small residual perception of taste stimuli. Especially for them, the seasoning of food can be useful. In general, it is advisable to eat a healthy, varied diet to prevent deficiencies, which in turn can impair the sense of taste.

Anyone who eats too little because of ageusia and has therefore already lost a lot of weight should go to a nutritional counselor.

In the case of all tasting disorders, it is advisable to abstain from nicotine and other substances that impair the ability to taste. Your doctor can advise you on this in more detail.

Pay attention to proper oral hygiene (regular brushing, flossing, etc.). This helps to prevent infections (e.g. with bacteria or fungi), which can damage the mucous membrane (and thus also the taste buds).