Q. I lost my sense of taste and smell after a bad cold several months ago. This happened once before after a bout with the flu, but my ability to taste and smell returned after a few weeks. Could this loss be because of my age -- 68 -- or a vitamin deficiency?

A. It sounds like you had a bad viral infection that damaged your sense of smell. Because the sense of taste depends very much on having a good sense of smell, your taste is also affected.

Viral infections, such as colds, the flu and sinusitis, can temporarily impair the sense of smell. Everyone has had the experience of not being able to taste foods when their nose was stuffed up because of a cold or allergies. Luckily, allergies and most infections don't result in lasting problems.

Sometimes, however, a viral infection can permanently damage the delicate nerves of smell in your nose. If so, you may suffer from partial or complete loss of smell and impaired taste. Once these nerves are destroyed, not much can be done to restore your sense of smell.

Other conditions can affect these two complementary senses. As you grow older, your sense of smell and taste tends to diminish, especially after age 70. Lack of certain nutrients, particularly zinc and vitamin A, can impair these senses, but zinc and vitamin A deficiency are not that common in the U.S.

Tumors of the front of the brain or in the nose can put pressure on the nerves of smell and lead to impaired or distorted smell, for example, smelling unusual odors. A CT scan of the skull may be in order if you have an otherwise unexplained loss of smell.

Besides viral infections, one of the most common reasons for losing your sense of smell is injury to your nose or front of your head. Serious head injury often snaps the delicate nerves of smell as they travel from your nose to the smell center in the front of your brain. Once damaged in this way, your sense of smell is not likely to return.

Certain medications can alter your sense of smell, and many drugs can affect your sense of taste. For example, they may give you a bitter, unpleasant or metallic taste. Your doctor should go over your medicines with you to make sure none of them is contributing to your problem.

Besides medicines, smoking cigarettes will impair your sense of taste and smell. In fact, the reason some people may gain weight after they stop smoking is that they regain their sense of taste and enjoy eating more. It probably goes without saying that snorting cocaine or other harmful substances can damage your nose and sense of smell.

People with a dry mouth from medication or underlying medical condition such as Sjo gren's syndrome (which causes dry mouth and dry eyes, among other problems) may lose some ability to taste. If this is the cause of your problem, artificial saliva may help.

If the reason for your loss of taste or smell isn't known and your condition hasn't responded to treatment, you might ask your doctor to refer you to the nationally recognized Taste and Smell Clinic, which specializes in disorders of taste and smell. It is located at 5125 MacArthur Blvd. NW, Suite 20, Washington, D.C. 20016 (1-202-364-8921).

Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.