Smell Disorders

• How does our sense of smell work?
• What are the smell disorders?
• What causes smell disorders?
• How are smell disorders diagnosed?
• Are smell disorders serious?
• Can smell disorders be treated?
• What research is being done?
• What can I do to help myself?

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.

How does our sense of smell work?

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.

What are the smell disorders?

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.

What causes smell disorders?

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.

How are smell disorders diagnosed?

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.

Are smell disorders serious?

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.

Can smell disorders be treated?

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.

What research is being done?

The NIDCD (National Institute on Deafness and Other Communication Disorders) 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.