Most of us take our sense of smell for granted. But have you ever thought about what it would be like to not be able to smell something? The complete loss of smell is called anosmia (an-OHZ-me-uh). Without your sense of smell, food tastes different, you can’t smell the scent of a flower, and you could find yourself in a dangerous situation, unknowingly. For example, without the ability to detect odors, you wouldn’t smell a gas leak, smoke from a fire, or sour milk.

Fortunately, for most people, anosmia is a temporary nuisance caused by a severely stuffy nose from a cold. Once the cold runs its course, a person’s sense of smell returns.

But for some people, including many elderly, the loss of a sense of smell may persist. In addition, anosmia can be a sign of a more serious medical condition. Any ongoing problems with smell should be checked out by a doctor.

A person’s sense of smell is driven by certain processes. First, a molecule released from a substance (such as fragrance from a flower) must stimulate special nerve cells (called olfactory cells) found high up in the nose. These nerve cells then send information to the brain, where the specific smell is identified. Anything that interferes with these processes, such as nasal congestion, nasal blockage, or damage to the nerve cells themselves, can lead to loss of smell.

The ability to smell also affects our ability to taste. Without the sense of smell, our taste buds can only detect a few flavors, and this can affect your quality of life.

Nasal congestion from a cold, allergy, sinus infection, or poor air quality is the most common cause of anosmia. Other anosmia causes include:

• Nasal polyps — small noncancerous growths in the nose and sinusesthat block the nasal passage.
• Injury to the nose and smell nerves from surgery or head trauma.
• Exposure to toxic chemicals, such as pesticides or solvents.
• Certain medications, including antibiotics, antidepressants, anti-inflammatory medication, heart medications, and others.
• Cocaine abuse.
• Old age. Like vision and hearing, your sense of smell can become weaker as you age. In fact, one’s sense of smell is most keen between the ages of 30 and 60 and begins to decline after age 60.
• Certain medical conditions, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, nutritional deficiencies, congenital conditions, and hormonal disturbances.
• Radiation treatment of head and neck cancers.

The obvious sign of anosmia is a loss of smell. Some people with anosmia notice a change in the way things smell. For example, familiar things begin to lack odor.

If nasal congestion from a cold or allergy is the cause of anosmia, treatment is usually not needed, and the problem will get better on its own. Short-term use of over-the-counter decongestants may open up your nasal passages so that you can breathe easier. However, if the congestion gets worse or does not go away after a few days, see your doctor. You may have an infection and need antibiotics, or another medical condition may be to blame.