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Taste and 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. If you would like more information about your sense of
smell, the fact sheet Smell and Smell Disorders
may answer some of your questions.
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.
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.
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.
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.
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.
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.
The
NIDCD supports basic and clinical investigations of chemosensory disorders
at institutions across the Nation. Some of these studies are conducted at
several chemosensory research centers, where scientists work together to
unravel the secrets of taste disorders.
Some of the most recent research on our sense of taste focuses on
identifying the key receptors in our taste cells and how they work in
order to form a more complete understanding of the gustatory system,
particularly how the protein mechanisms in G-protein-coupled receptors
work. Advances in this area may have great practical uses, such as the
creation of medicines and artificial food products that allow older adults
with taste disorders to enjoy food again. Future research may examine how
tastes change in both humans and animals. Some of this research will focus
on adaptive taste changes over long periods in different animal species,
while other research will examine why we accept or have an aversion to
different tastes. Beyond this, scientists feel future gustatory research
may also investigate how taste affects various processing activities in
the brain. Specifically, how taste interacts with memory, influences
hormonal feedback systems, and its role in the eating decisions and
behavior.
Already, remarkable progress has been made in establishing the nature
of changes that occur in taste senses with age. It is now known that age
takes a much greater toll on smell than on taste. Also, taste cells (along
with smell cells) are the only sensory cells that are regularly replaced
throughout a person's life span--taste cells usually last about 10 days.
Scientists are examining these phenomena which may provide ways to replace
damaged sensory and nerve cells.
NIDCD's research program goals for chemosensory sciences include
- Promoting the regeneration of sensory and nerve cells
- Appreciating the effects of the environment (such as gasoline fumes,
chemicals, and extremes of relative humidity and temperature) on taste.
- Preventing the effects of aging.
- Preventing infectious agents and toxins from reaching the brain
through the olfactory nerve.
- Developing new diagnostic tests.
- Understanding associations between chemosensory disorders and
altered food intake in aging as well as in various chronic illnesses.
- Improving treatment methods and rehabilitation strategies.
Proper
diagnosis by a trained professional, such as an otolaryngologist, is
important. These physicians specialize in disorders of the head and neck,
especially those related to the ear, nose, and throat. Diagnosis may lead
to treatment of the underlying cause of the disorder. Many types of taste
disorders are curable, and for those that are not, counseling is available
to help patients cope.
NIH Publication No. 01-3231A
Updated March 2002
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