often experience general reductions in chemosen-
sory perceptions.
Physical obstructions The most common cause
of taste and smell disturbances is congestion,
which blocks contact between odor molecules and
odor sensors in the nose. Congestion results from
a wide range of circumstances, most of which are
temporary or transient (come and go). These
include COLDS,ALLERGIC RHINITIS(seasonal allergies),
and SINUSITIS. Mechanical obstructions such as
nasal polyps or SEPTAL DEVIATIONalter the flow of
air through the nose so that odor molecules pass
by only a small section of the olfactory epithelium,
the patch of nerve endings extending from the
olfactory bulb. Dental problems that cause irrita-
tion in the MOUTH, especially of the tongue, can
disrupt the functions of taste cells.
Aging The aging process is the second-leading
cause of diminished taste and smell. Researchers
estimate that diminished chemosensory percep-
tion affects more than half of people over age 65;
by age 80 the loss is significant enough to interfere
with the desire to eat. The olfactory epithelium in
the nose loses about 1 percent of its nerve cells
each year. Though the tongue renews taste buds
every few weeks throughout most of life, the rate
of replacement slows in the later decades. By age
80, the number of taste cells in the mouth has
diminished by as much as 40 percent. In combina-
tion with the loss of olfactory nerve endings, there
often is the perception of complete inability to
perceive flavors.
Health conditions and medication side effectsMany health conditions can cause disturbances of
smell and taste. Among those most frequently
implicated are diabetes, hypertension, SARCOIDOSIS,
BELL’S PALSY, Parkinson’s disease, ALZHEIMER’S DIS-
EASE, and MULTIPLE SCLEROSIS. Olfactory auras (per-
ceptions of smells) often precede migraine
headaches and epileptic seizures. Numerous med-
ications affect taste and smell, notably ANTIBIOTIC
MEDICATIONS, levodopa (to treat Parkinson’s dis-
ease), angiotensin-converting enzyme (ACE)
inhibitors (antihypertensive medications), “statin”
lipid-lowering medications, and CHEMOTHERAPY
agents such as cisplatin and methotrexate. Taste
and smell usually return to normal after stopping
the medication, though chemotherapy-related
changes may persist or become permanent. RADIA-
TION THERAPY to the head or neck also alters
chemosensory perception, often permanently.
Nerve damage Smell and taste disturbances can
result from damage to the nerves that carry
chemosensory messages to the brain, such as
might occur with injury or neurologic diseases.
The first cranial nerve (olfactory nerve) carries
most odor messages to the brain, with the fifth
cranial nerve (trigeminal nerve) conveying limited
signals. Three CRANIAL NERVES—the seventh (facial
nerve), ninth (glossopharyngeal nerve), and tenth
(vagus nerve)—convey taste messages to the
brain. Trauma such as from a BROKEN NOSEcan
damage the olfactory nerve endings in the roof of
the nose. Chronic exposure to cigarette smoke or
inhaled drugs (notably cocaine as well as cortico-
steroid nasal sprays used to treat ASTHMAand aller-
gic rhinitis) also damages these hairlike structures.Treatment Options and Outlook
Treatment for smell and taste disorders targets the
underlying causes of the disturbances to the
extent doctors can identify them. Approaches
include- reducing exposure to environmental irritants
such as cigarette smoke and allergens - treating chronic sinusitis, dental disease, and
allergic rhinitis - removing nasal polyps and correcting septal
defects in the nose - evaluating regular medications being taken to
identify any that can interfere with smell and
taste - looking for patterns of chemosensory distur-
bance
Often, idiopathic taste and smell disturbances
(those of undetermined cause) improve on their
own over time. Changes due to diseases tend to
follow the course of the underlying condition,
progressively worsening along with the principal
condition, as in Parkinson’s disease or multiple
sclerosis.Risk Factors and Preventive Measures
Treating infections promptly and avoiding irritants
that interfere with olfactory and gustatory func-smell and taste disturbances 53