NIDCD Fact Sheet

Smell Disorders

u.s. department of health & human services ∙ national institutes of health ∙ National Institute on Deafness and Other Communication Disorders smell taste

How common are smell disorders?

Our sense of smell helps us enjoy life. We delight in 

the aromas of our favorite foods or the fragrance of 

flowers. Our sense of smell is also a warning system, 

alerting us to danger signals such as a gas leak, spoiled 

food, or a fire. Any loss of our sense of smell can have 

a negative effect on our quality of life. It also can be a 

sign of more serious health problems.

Roughly 1–2 percent of people in North America 

say that they have a smell disorder. Problems with 

smell increase as people get older, and they are more 

common in men than women. In one study, nearly 

one-quarter of men ages 60–69 had a smell disorder, 

while about 11 percent of women in that age range 

reported a problem.

Many people who have smell disorders also notice 

problems with their sense of taste. To learn more 

about your sense of taste, read the NIDCD fact sheet 

Taste Disorders at http://www.nidcd.nih.gov/health/

smelltaste/taste.asp. 

How does our sense of smell work?

Our sense of smell—like our sense of taste—is part of 

our chemosensory system, or the chemical senses. 

Specialized sensory cells, called olfactory sensory 

neurons, are found in a small patch of tissue high 

inside the nose. These cells connect directly to the 

brain. Each olfactory neuron expresses one odor 

receptor. Microscopic molecules released by substances 

around us—whether it’s coffee brewing or a pine 

forest—stimulate these receptors. Once the neurons 

detect the molecules, they send messages to our brain, 

which identifies the smell. (Because there are more 

smells in the environment than there are receptors, 

a given molecule may stimulate a combination of 

receptors. This response is registered by the brain as a 

particular smell.)

Smells reach the olfactory sensory neurons via two 

pathways. The first pathway is through our nostrils. 

The second pathway is through a channel that 

connects the roof of the throat region to the nose. 

When we chew our food, aromas are released that 

access the olfactory sensory neurons through this 

channel. If the channel is blocked, such as when our 

noses are stuffed up from a cold or flu, odors cannot 

reach the sensory cells and much of our ability to enjoy 

a food’s flavor is lost. In this way, our senses of smell 

and taste work closely together. Without the olfactory 

sensory neurons, familiar flavors such as chocolate or 

oranges would be hard to distinguish. Some people 

who go to the doctor because they think they’ve lost 

their sense of taste are surprised to learn that they 

have a smell disorder instead.

Our sense of smell is also influenced by something 

called the common chemical sense. This sense involves 

thousands of nerve endings, especially on the moist 

surfaces of the eyes, nose, mouth, and throat. These 

nerve endings help us sense irritating substances 

such as the tear-inducing power of an onion or the 

refreshing cool of peppermint. 
NIDCD Fact Sheet

Smell Disorders

What are the smell disorders?

People who experience smell disorders either have a 

loss in their ability to smell or changes in the way they 

perceive odors. Hyposmia is a reduced ability to detect 

odors. Anosmia is the inability to detect odors at all. 

People who experience changes in how they sense 

odors may notice that familiar odors are distorted or 

that something that normally smells pleasant now 

smells foul. Other people may sense an odor that isn’t 

present at all.

What causes smell disorders?

Smell disorders have many causes, with some more 

obvious than others. Most people who develop a smell 

disorder have experienced a recent illness or injury. 

Common causes of smell disorders are:

• Sinus and other upper respiratory infections

• Polyps in the nasal cavities

• Frontal head injuries

• Hormonal disturbances

• Dental problems

• Exposure to certain chemicals, such as insecticides 

and solvents

• Numerous medications, including some common 

antibiotics and antihistamines

• Radiation associated with the treatment of head 

and neck cancers

• Aging

• Other health issues that affect the nervous system, 

such as Parkinson’s disease or Alzheimer’s disease

In 2009, the U.S. Food and Drug Administration 

warned consumers to stop using several popular cold 

remedies because they could result in the loss of smell. 

Smoking also can interfere with our sense of smell. 

How are smell disorders diagnosed?

Both smell and taste disorders are treated by an 

otolaryngologist, a doctor who specializes in diseases 

of the ear, nose, throat, head, and neck. Some tests 

are designed to measure the smallest amount of 

odor that patients can detect. Another common test 

consists of a booklet of sheets that contain tiny beads 

filled with specific odors. Patients are asked to scratch 

each sheet and identify the odor. 

An accurate assessment of your smell disorder will 

include, among other things, a physical examination 

of your ears, nose, and throat; a review of your 

health history, such as exposure to toxic chemicals or 

trauma; and a smell test supervised by a health care 

professional. 

Are smell disorders serious?

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, spoiled food, or the odor of a natural 

gas leak or dangerous fumes. 

When smell is impaired, some people change their 

eating habits. Some may eat too little and lose weight 

while others may eat too much and gain weight. Food 

becomes less enjoyable and people may use too much 

salt to improve the taste. This can be a problem for 

people with certain medical conditions, such as high 

blood pressure or kidney disease. In severe cases, loss 

of smell can lead to depression. 

smelltaste
olfactory receptor genes that encode the receptors 

found on olfactory sensory neurons—one receptor 

per neuron. Recent studies on how olfactory sensory 

neurons recognize odors, aided by new technology, 

are revealing how our olfactory system detects and 

identifies the differences between the many chemical 

compounds that form odors. 

Like our sense of taste, our sense of smell can be 

damaged by certain medicines. However, other 

medications, especially those prescribed for allergies, 

may improve the sense of smell. NIDCD-supported 

scientists are working to find out why this is so in an 

effort to develop drugs that can help restore a person’s 

sense of smell.

NIDCD-supported researchers have found that the loss 

of smell affects the choices an older person makes 

about eating certain foods. Food choices impact diet 

and overall health. They are looking at how and why 

this takes place in order to develop more effective 

ways to help older people—especially those with 

chronic illnesses—cope better with problems with 

smell and to maintain proper nutrition.

Olfactory sensory neurons—as well as sensory cells 

that help us taste—are the only sensory cells that our 

bodies regularly replace. Scientists are exploring why 

and how this happens so that they might find ways to 

replace other damaged sensory and nerve cells. 

NIDCD-supported chemosensory scientists are 

exploring how to:

• Promote the regeneration of sensory and 

nerve cells. 

• Understand the effects of the environment (such as 

gasoline fumes, chemicals, and extremes of relative 

humidity and temperature) on smell and taste. 

more

Problems with our chemical senses may be a sign of 

other serious health conditions. A smell disorder can 

be an early sign of Parkinson’s disease, Alzheimer’s 

disease, or multiple sclerosis. It also can accompany 

or signal obesity, diabetes, hypertension, and 

malnutrition. If you are experiencing a smell disorder, 

consult your physician. 

Can smell disorders be treated?

Many types of smell disorders are curable, and for 

those that are not, counseling is available to help 

people adjust to the problem. 

Diagnosis by a doctor is important to identify and treat 

the underlying cause of a potential smell disorder. If 

your problem is caused by certain medications, talk to 

your doctor to see if lowering the dosage or changing 

that medicine may reduce its effect on your sense of 

smell. Surgery to remove nasal obstructions such as 

polyps can restore airflow. Some people recover their 

ability to smell when the illness causing their olfactory 

problem is resolved. Occasionally, a person may 

spontaneously recover his or her sense of smell. 

What research is being done?

The National Institute on Deafness and Other 

Communication Disorders (NIDCD) supports basic and 

clinical investigations of smell and taste disorders at 

institutions across the nation. Some of these studies 

are conducted at chemosensory research centers, 

where scientists are making discoveries 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. In 2004, NIDCD 

grantee Linda B. Buck, Ph.D., together with Richard 

Axel, M.D., received the Nobel Prize in Physiology or 

Medicine for their discovery of a family of about 1,000 
NIDCD supports and conducts research and research training on the 

normal and disordered processes of hearing, balance, smell, taste, 

voice, speech, and language and provides health information, based 

upon scientific discovery, to the public.

NIDCD Fact Sheet: Smell Disorders

Publication No. 09-3231

Updated July 2009

For more information, contact:

NIDCD Information Clearinghouse

1 Communication Avenue

Bethesda, MD 20892-3456

Toll-free Voice: (800) 241-1044

Toll-free TTY: (800) 241-1055

E-mail: nidcdinfo@nidcd.nih.gov

Internet: http://www.nidcd.nih.gov

The NIDCD Information Clearinghouse is a service of the 

National Institute on Deafness and Other Communication 

Disorders, National Institutes of Health, U.S. Department 

of Health and Human Services.

hearing, balancevoice, speech, language

• Prevent the effects of aging on smell and taste. 

• Prevent infectious agents and toxins from reaching 

the brain through the olfactory nerve. 

• Develop new diagnostic tests for taste and 

smell disorders. 

• Understand associations between chemosensory 

disorders and altered food intake in aging as well as 

in various chronic illnesses. 

• Improve treatment methods and rehabilitation 

strategies. 

What can I do if I think I have a 

smell disorder?

Proper diagnosis by a health professional, such as an 

otolaryngologist, is important. Diagnosis may lead 

to an effective treatment of the underlying cause of 

your smell disorder. Many types of smell disorders are 

curable. For those that are not, counseling is available 

to help patients cope. 

smell, taste 

Where can I find more information?

The NIDCD maintains a directory of organizations that 

can answer questions and provide printed or electronic 

information about hearing, balance, smell, taste, voice, 

speech, and language. This directory is available at 

http://www.nidcd.nih.gov/directory.

To find organizations with information specifically 

about smell disorders, click on “Smell and Taste” in the 

“Browse by Topic” list. 

For more information, additional addresses and phone 

numbers, or a printed list of organizations, contact:

NIDCD Information Clearinghouse

1 Communication Avenue

Bethesda, MD 20892-3456

Toll-free Voice: (800) 241-1044

Toll-free TTY: (800) 241-1055

Fax: (301) 770-8977

E-mail: nidcdinfo@nidcd.nih.gov