Smell and Taste Disorders
If you experience
a smell or taste problem, it is important to remember that you
are not alone: thousands of other individuals have faced the
same situation. More than 200,000 persons visit a physician
for a smell or taste problem each year. Many more smell and
taste disturbances go unreported.
How do smell and
taste work?
Smell and taste belong
to our chemical sensing system, or the chemosenses. The complicated
processes of smelling and tasting begin 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 smells or
tastes are identified.
Olfactory or smell
nerve cells are stimulated by the odors around us--the fragrance
from a gardenia or the smell of bread baking. These nerve cells
are found in a small patch of tissue high inside the nose, and
they connect directly to the brain.
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 and throat.
Many of the small bumps that can be seen on the tongue contain
taste buds.
A third chemosensory
mechanism, called the common chemical sense, contributes to
our senses of smell and taste. 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
four basic taste sensations: sweet, sour, bitter, and salty.
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. 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 foods sweetness or bitterness. That's because the familiar
flavor of chocolate is sensed largely by odor. So is the well-known
flavor of coffee.
What are the smell
and taste disorders?
The most common chemosensory
complaints are a loss of the sense of smell and the sense of
taste. Testing may demonstrate a reduced ability to detect odors
(hyposmia) or to taste sweet, sour, bitter, or salty
substances (hypogeusia). Some people can detect no odors
(anosmia) or no tastes (ageusia).
In other disorders
of the chemical senses, the system may misread and distort an
odor, a taste, or a flavor. Or a person may detect a foul odor
or taste from a substance that is normally pleasant smelling
or tasting.
Overall, smell disorders
are more common than taste disorders. They rarely occur together.
What causes smell
and 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
smell or taste problems.
Chemosensory disorders
may result from polyps in the nasal cavities, sinus infections,
hormonal disturbances, or dental problems. Loss of smell and
taste also can be caused by exposure to certain chemicals such
as insecticides and by some medicines.
Many patients who
receive radiation therapy for cancers of the head and neck develop
chemosensory disturbances.
How are smell
and 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
also may be asked to compare the smells or tastes of different
chemicals or to note how the intensities of smells or tastes
grow when a chemicals concentration is increased.
Scientists have developed
an easily administered A scratch and sniff test to evaluate
the sense of smell. A person scratches pieces of paper treated
to release different odors, sniffs them, and tries to identify
each odor from a list of possibilities.
In taste testing,
the patient responds to different chemical concentrations: this
may involve a simple A sip, spit, and rinse test, or chemicals
may be applied directly to specific areas of the tongue.
Are smell and
taste disorders serious?
A person with faulty
chemosenses is deprived of an early warning system that most
of us take for granted. Smell and taste alert us to fires, poisonous
fumes, leaking gas, and spoiled food and beverages. Smell and
taste losses can also lead to depression.
Abnormalities in
smell and taste functions frequently 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 Parkinsons disease, Alzheimers
disease, and Korsakoffs psychosis.
Can smell and
taste disorders be treated?
If a certain medication
is the cause of a smell or taste disorder, stopping or changing
the medicine may help eliminate the problem. Some patients,
notably those with respiratory infections or allergies, regain
their smell or taste upon the resolution of their illness. In
many cases, nasal obstructions such as polyps can be removed
surgically to restore airflow to the nose. Often the correction
of a general medical problem can also correct the loss of smell
and taste. Occasionally, recovery of the chemosenses occurs
spontaneously.
What research
is being done?
The National Institute
on Deafness and Other Communication Disorders (NIDCD), one of
the thirteen institutes of the National Institutes of Health,
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 smell and taste disorders.
Remarkable progress
has been made in establishing the nature of changes that occur
in the chemical senses with age. It is now known that age takes
a much greater toll on smell than on taste. Scientists have
found that the sense of smell begins to decline after age 60.
Women at all ages are generally more accurate than men in identifying
odors. Smoking can adversely affect the ability to identify
odors in both men and women.
Although certain
medications can cause chemosensory problems, others--notably
anti-allergy drugs--seem to improve the senses of smell and
taste. Scientists are working to find medicines similar to anti-allergy
drugs that can be used to treat patients with chemosensory losses.
Smell and taste cells
are the only sensory cells that are regularly replaced throughout
the life span. Scientists are examining these phenomena which
may provide ways to replace these and other damaged sensory
and nerve cells.
NICHD's research
program goals for chemosensory sciences include:
- promotion of the
regeneration of sensory and nerve cells
- appreciating the
effects of the environment on smell and taste (such as gasoline
fumes, chemicals, and extremes of relative humidity and temperature)
- prevention of
the effects of aging
- prevention of
the access of infectious agents and toxins to the brain through
the olfactory nerve
- development of
new diagnostic tests
- understanding
associations between chemosensory disorders and altered food
intake in aging as well as in various chronic illnesses
- improved methods
of treatment and rehabilitation strategies
What can I
do to help myself?
Proper diagnosis
by a trained professional for example, an otolaryngologist-head
and neck surgeon, 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 an underlying cause of the disturbance. Many types of
smell and taste disorders are curable, and for those that
are not, counseling is available to help patients cope with
a disorder.
NIH Publication No. 92-3231
Date: June 199
|
.gif)
