Smell and Taste Disorders (Chemosensory Disorders)

The processes of smelling and tasting are complex. They begin when molecules are released into the air we breathe or dissolve into our saliva or nasal mucus from fragrances or foods.  These molecules then stimulate the sensory cells in the nose, mouth, or throat.

Olfactory nerve cells are stimulated by odors. They are located high inside the nose, and connect directly to the brain. They sit very superficially inside the lining of the nose.  This is good so they can sense odor molecules more easily, but unfortunately this also puts them at greater risk for injury.

Gustatory nerve cells are located in the taste buds of the mouth and throat, and are limited to sensing the five basic tastes of sweet, sour, bitter, salty and umami.

Another chemosensory process, called common chemical sense, also contributes to smell and taste. These cells alert the brain to sensations such as heat (as from spicy peppers) or cool (as from menthol or mint). 

What we think of as the “flavor” of our food is actually a combination of all these senses working together.  Taste is 80% dependent on olfaction, so without the ability to smell, all food and drink can only be sensed as one of those five basic tastes, with no other differentiation possible.
 

Source: National Institute on Deafness and Other Communication Disorders

The decrease or complete loss of the sense of smell (hyposmia or anosmia) and taste (hypogeusia or ageusia) are the most common chemosensory disorders.

In other disorders of the chemosenses, odors, tastes, or flavors may be misread or distorted, causing a person to detect an unpleasant odor or taste from something that is normally pleasant to taste or smell.

Smell disorders are serious because they damage the early warning system that can alert a person to such things as:

• fire
• poisonous fumes
• leaking gas
• spoiled food and beverages

Abnormalities in taste and smell can accompany or indicate the existence of diseases or conditions such as:

• obesity
• diabetes
• hypertension
• malnutrition
• degenerative diseases of the nervous system such as Parkinson's disease and Alzheimer's disease

Although some people are born with chemosensory disorders, and there are actually over 100 reasons why people can lose their smell and taste, most are caused by:

• illness (i.e., common cold, upper respiratory infection, sinus infection)
• injury to the head
• hormonal disturbances
• dental problems
• exposure to certain chemicals
• certain medications
• exposure to radiation therapy for head or neck cancer

In addition to a complete medical history and physical examination, diagnostic procedures may include:

• imaging such as a CT scan or MRI
• measuring the lowest concentration of a chemical that a person can recognize
• comparing tastes and smells of different chemicals
• "scratch and sniff" tests
• "sip, spit, and rinse" tests where chemicals are directly applied to specific areas of the tongue

At the Stanford Sinus Center, Dr. Zara M. Patel has a special interest in evaluating and treating patients who have a decrease in or complete loss of smell. 

Specific treatments for smell and taste disorders will be determined based on:

• your age, overall health, and medical history
• extent of the disorder
• your tolerance for specific medications, procedures, or therapies
• duration and subsequent prognosis of the disorder
• your opinion or preference

Treatment may include:

• stopping or changing medications that contribute to the disorder
• correction of the medical problem that is causing the disorder
• surgical removal of obstructions that may be causing the disorder
• olfactory training
• counseling