How Common Are Smell and Taste Disorders?
One study estimates that more than two million Americans have smell and taste
disorders. Another estimate suggests that more than 200,000 people visit a physician
for a smell or taste problem each year. Many more smell and taste disturbances
go unreported. A person with a faulty sense of smell and taste 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 foods. Loss of the sense
of smell may also be a sign of sinus disease, growths in the nasal passages or,
in rare circumstances, brain tumors. Because an intact sense of smell and taste
is required in some professions, chefs and firemen, among others, may be subject
to serious economic hardship.
How Do Smell and Taste Work?
Smell and taste belong to our chemical sensing system, or chemosensation. The
complicated processes of smelling and tasting begin when molecules released
by the substances around us stimulate special nerve cells in the nose, mouth
or throat. These cells transmit messages to the brain, where specific smells
or tastes are identified.
Olfactory (smell nerve) cells are stimulated by the odors around us - the
fragrance from a rose, the smell of bread baking. These nerve cells are found
in a tiny patch of tissue high up in the nose, and they connect directly to
Taste cells react to food or drink mixed with saliva and 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. These surface cells send taste information
to nearby nerve fibers, which send messages to the brain.
Taste and smell cells are the only cells in the nervous system that are replaced
when they become old or damaged. Scientists are examining this phenomenon while
studying ways to replace other damaged nerve cells.
A third chemosensory mechanism, called the common chemical sense, contributes
to our senses of smell and taste. In this system, thousands of free nerve endings
- especially on the moist surfaces of the eyes, nose, mouth and throat - identify
sensations like the sting of ammonia, the coolness of menthol and the "heat" of
We can commonly identify four basic taste sensations: sweet, sour, bitter
and salty. Certain combinations of these tastes - along with texture, temperature,
odor and the sensations from the common chemical sense - produce a flavor.
It is flavor that lets us know whether we are eating peanuts or caviar.
Many 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. This is because the familiar flavor of chocolate is sensed largely
by odor. So is the well-known flavor of coffee. This is why a person who wishes
to fully savor a delicious flavor (i.e., an expert chef testing his own creation)
will exhale through his nose after each swallow.
What Causes Smell and Taste Disorders?
The predominant problem is a natural decline in smelling ability that typically
occurs after age 60. Scientists have found that the sense of smell is most
accurate between the ages of 30 and 60 years. It begins to decline after age
60, and a large proportion of elderly persons have lost their smelling ability.
Women of all ages are generally more accurate than men in identifying odors.
Some people are born with a poor sense of smell or taste, but most patients
develop them after an injury or illness. Upper respiratory infections are blamed
for some losses, and injury to the head can also cause smell or taste problems.
Loss of smell and taste may result from polyps in the nasal or sinus cavities,
hormonal disturbances or dental problems. They can also be caused by prolonged
exposure to certain chemicals such as insecticides and by some medicines.
Tobacco smoking is the most concentrated form of pollution that most people
will ever be exposed to. It impairs the ability to identify odors and diminishes
the sense of taste. Quitting smoking improves the smell function, but very
slowly. For example: Two-pack-a-day smokers must quit for as many years as
they smoked to completely restore their sense of smell.
Many patients who receive radiation therapy for cancers of the head and neck
later complain of lost smell and taste. They can also be lost in the course
of some diseases of the nervous system.
Patients who have lost their larynx or "voice box" commonly complain
of poor ability to smell and taste. These senses are greatly improved when
laryngectomy patients use a special "bypass" tube to breathe through
the nose again rather than through an opening in the neck. (This emphasizes
the contribution of air flow through the nose for smell and taste.)
How Are Smell and Taste Disorders Diagnosed?
The extent of loss of smell or taste can be tested with a measurement of the
lowest concentration of a chemical that a person can accurately detect and
recognize. A patient may also be asked to compare the smells or tastes of different
chemicals, the intensities of smells or taste of different chemicals, or how
the intensities of smells or tastes grow when a chemical's concentration is
Scientists have developed an easily administered "scratch-and sniff" test
to evaluate the sense of smell. A person scratches pieces of treated paper
to release different odors, sniffs them, and tries to identify each odor from
a list of possibilities. In taste testing, the patient reacts 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.
Can Smell and Taste Disorders Be Treated?
Sometimes a certain medication is the cause of a smell or taste disorder, and
improvement occurs when that medicine is stopped or changed. Although certain
medications can cause chemosensory problems, others - particularly anti-allergy
drugs - seem to improve the senses of taste and smell. Some patients - notably
those with serious respiratory infections or seasonal allergies - regain their
smell or taste simply by waiting for their illness to run its course. In many
cases, nasal obstructions such as polyps can be removed to restore airflow
to the receptor area and can correct the loss of smell and taste. OccasionaIly,
chemosenses return to normal just as spontaneously as they disappeared.
What Can I Do To Help Myself?
If you experience a smell or taste problem, try to identify and record the
circumstances surrounding it. When did you first become aware of it? Did you
have a "cold" or "flu" then? A head injury? Were you exposed
to air pollutants, pollens, danders or dust to which you might be allergic?
Is this a recurring problem? Does it come in any special season, like hayfever
Bring all this information with you when you visit a physician who deals with
diseases of the nose and throat. Also be prepared to tell him about your general
health and any medications you are taking. Proper diagnosis by a trained professional
can provide reassurance that your illness is not imaginary. You may even be
surprised by the results. For example, what you may think is a taste problem
could actually be a smell problem, because much of what you think you taste
you really smell.
Diagnosis may also lead to treatment of an underlying cause for the disturbance.
Many types of smell and taste disorders are reversible, but if yours is not,
it is important to remember that you are not alone: thousands of other patients
have faced the same situation.
If you have further questions about Smell and Taste, please feel free to contact
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