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Smell and Smell Disorders
Every year, thousands of people develop problems with their sense of
smell. In fact, more than 200,000 people visit a physician each year for
help with smell disorders or related problems. If you experience a problem
with your sense of smell, call your doctor. This fact sheet explains smell
and smell disorders.
Many people who have smell disorders also notice problems with their
sense of taste. If you would like more information about your sense of
taste, the fact sheet Taste and Taste Disorders
may answer some of your questions.
The sense of smell is part of our chemical sensing
system, or the chemosenses. Sensory cells in our nose, mouth, and throat
have a role in helping us interpret smells, as well as taste flavors.
Microscopic molecules released by the substances around us (foods,
flowers, etc.) stimulate these sensory cells. Once the cells detect the
molecules they send messages to our brains, where we identify the smell.
Olfactory, or smell nerve cells, are stimulated by the odors around
us--the fragrance of 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. Our sense of smell is also influenced by
something called the common chemical sense. This sense involves nerve
endings in our eyes, nose, mouth, and throat, especially those on moist
surfaces. Beyond smell and taste, these nerve endings help us sense the
feelings stimulated by different substances, such as the eye-watering
potency of an onion or the refreshing cool of peppermint.
It's a surprise to many people to learn that flavors are recognized
mainly through the sense of smell. Along with texture, temperature, and
the sensations from the common chemical sense, the perception of flavor
comes from a combination of odors and taste. Without the olfactory cells,
familiar flavors like coffee or oranges would be harder to distinguish.
People
who experience smell disorders experience either a loss in their ability
to smell or changes in the way they perceive odors. As for loss of the
sense of smell, some people have hyposmia, which is when their
ability to detect odor is reduced. Other people can't detect odor at all,
which is called anosmia. As for changes in the perception of odors,
some people notice that familiar odors become distorted. Or, an odor that
usually smells pleasant instead smells foul. Still other people may
perceive a smell that isn't present at all.
Smell disorders have many causes, some clearer than others. Most
people who develop a smell disorder have recently experienced an illness
or an injury. Common triggers are upper respiratory infections and head
injuries.
Among other causes of smell disorders are polyps in the nasal cavities,
sinus infections, hormonal disturbances, or dental problems. Exposure to
certain chemicals, such as insecticides and solvents, and some medicines
have also been associated with smell disorders. People with head and neck
cancers who receive radiation treatment are also among those who
experience problems with their sense of smell.
Doctors and scientists have developed tests to determine the extent
and nature of a person's smell disorder. Tests are designed to measure the
smallest amount of odor patients can detect as well as their accuracy in
identifying different smells. In fact, an easily administered "scratch and
sniff" test allows a person to scratch pieces of paper treated to release
different odors, sniff them, and try to identify each odor from a list of
possibilities. In this way, doctors can easily determine whether patients
have hyposmia, anosmia, or another kind of smell disorder.
Yes. Like all of our senses, our sense of smell plays an important
part in our lives. The sense of smell often serves as a first warning
signal, alerting us to the smoke of a fire or the odor of a natural gas
leak and dangerous fumes. Perhaps more important is that our chemosenses
are sometimes a signal of serious health problems. Obesity, diabetes,
hypertension, malnutrition, Parkinson's disease, Alzheimer's disease,
multiple sclerosis, and Korsakoff's psychosis are all accompanied or
signaled by chemosensory problems like smell disorders.
Yes. Some people experience relief from smell disorders. Since certain
medications can cause a problem, adjusting or changing that medicine may
ease its effect on the sense of smell. Others recover their ability to
smell when the illness causing their olfactory problem resolves. For
patients with nasal obstructions such as polyps, surgery can remove the
obstructions and restore airflow. Not infrequently, people enjoy a
spontaneous recovery because olfactory neurons may regenerate following
damage.
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 are
making advances that help them understand our olfactory system and may
lead to new treatments for smell disorders.
Some of the most recent research into our sense of smell is also the
most exciting. Though a complete understanding of the uniquely
sophisticated olfactory system is still in progress, recent studies on how
receptors recognize odors, together with new technology, have revealed
some long-hidden secrets to how the olfactory system manages to detect and
discriminate between the many chemical compounds that form odors. Besides
uncovering the physical mechanisms our bodies use to accomplish the act of
identifying smell, these findings are helping scientists view the system
as a model for other molecular sensory systems in the body. Further,
scientists are confident that they are now laying the foundation to
understanding the finest details about our sense of smell--research that
may help them understand how smell affects and interacts with other
physiological processes.
Since scientists began studying the olfactory system, much has been
discovered about how our chemosenses work, especially in how they're
affected by aging. Like other senses in our bodies, our sense of smell can
be greatly affected simply by our growing older. In fact, 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, although
smoking can adversely affect that ability in both men and women.
Another area of discovery has been the olfactory system's reaction to
different medications. Like our sense of taste, our sense of smell can be
damaged by certain medicine. Surprisingly, other medications, especially
those prescribed for allergies, have been associated with an improvement
of the sense of smell. Scientists are working to find out why this is so
and develop drugs that can be used specifically to help restore the sense
of smell to patients who've lost it. Also, smell cells (along with 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.
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 smell
and 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.
The
best thing you can do is see a doctor. 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 an effective treatment of
the underlying cause of your smell disorder. Many types of smell disorders
are curable, and for those that are not, counseling is available to help
patients cope.
NIH Publication No. 01-3231
Updated March 2002
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