Taste Disorders

If you experience a taste problem, it is important to remember that you are not alone. More than 200,000 people visit a physician for such a chemosensory problem each year. Many more taste disorders go unreported.

Many people who have taste disorders also notice problems with their sense of smell.

How does our sense of taste work?

Taste belongs to our chemical sensing system, or the chemosenses. The complex process of tasting begins when tiny molecules released by the substances around us stimulate special cells in the nose, mouth, or throat. These special sensory cells transmit messages through nerves to the brain, where specific tastes are identified.

Gustatory or taste cells react to food and beverages. These surface cells in the mouth send taste information to their nerve fibers. The taste cells are clustered in the taste buds of the mouth, tongue, and throat. Many of the small bumps that can be seen on the tongue contain taste buds.

Another chemosensory mechanism, called the common chemical sense, contributes to appreciation of food flavor. In this system, thousands of nerve endings--especially on the moist surfaces of the eyes, nose, mouth, and throat--give rise to sensations like the sting of ammonia, the coolness of menthol, and the irritation of chili peppers.

We can commonly identify at least five different taste sensations: sweet, sour, bitter, salty, and umami (the taste elicited by glutamate, which is found in chicken broth, meat extracts, and some cheeses). In the mouth, these tastes, along with texture, temperature, and the sensations from the common chemical sense, combine with odors to produce a perception of flavor. It is flavor that lets us know whether we are eating a pear or an apple. Some people are surprised to learn that flavors are recognized mainly through the sense of smell. If you hold your nose while eating chocolate, for example, you will have trouble identifying the chocolate flavor--even though you can distinguish the food's sweetness or bitterness. That is because the distinguishing characteristic of chocolate, for example, what differentiates it from caramel, is sensed largely by its odor.

What are the taste disorders?

The most common true taste complaint is phantom taste perceptions. Additionally, testing may demonstrate a reduced ability to taste sweet, sour, bitter, salty, and umami, which is called hypogeusia. Some people can detect no tastes, called ageusia. True taste loss is rare; perceived loss usually reflects a smell loss, which is often confused with a taste loss.

In other disorders of the chemical senses, the system may misread and or distort an odor, a taste, or a flavor. Or a person may detect a foul taste from a substance that is normally pleasant tasting.

What causes taste disorders?

Some people are born with chemosensory disorders, but most develop them after an injury or illness. Upper respiratory infections are blamed for some chemosensory losses, and injury to the head can also cause taste problems.

Loss of taste can also be caused by exposure to certain chemicals such as insecticides and by some medicines. Taste disorders may result from oral health problems and some surgeries (e.g. third molar extraction and middle ear surgery). Many patients who receive radiation therapy for cancers of the head and neck develop chemosensory disorders.

How are taste disorders diagnosed?

The extent of a chemosensory disorder can be determined by measuring the lowest concentration of a chemical that a person can detect or recognize. A patient may also be asked to compare the tastes of different chemicals or to note how the intensity of a taste grows when a chemical'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.

Are taste disorders serious?

Yes. A person with a taste disorder is challenged not only by quality-of-life issues, but also deprived of an early warning system that most of us take for granted. Taste helps us detect spoiled food or beverages and, for some, the presence of food to which we're allergic. Perhaps more serious, loss of the sense of taste can also lead to depression and a reduced desire to eat.

Abnormalities in chemosensory function may accompany and even signal the existence of several diseases or unhealthy conditions, including obesity, diabetes, hypertension, malnutrition, and some degenerative diseases of the nervous system such as Parkinson's disease, Alzheimer's disease, and Korsakoff's psychosis.

Can taste disorders be treated?

Yes. If a certain medication is the cause of a taste disorder, stopping or changing the medicine may help eliminate the problem. Some patients, notably those with respiratory infections or allergies, regain their sense of taste when the illness resolves. Often the correction of a general medical problem can also correct the loss of taste. Occasionally, recovery of the chemosenses occurs spontaneously.