DEAR DOCTOR K:

I am a 43-year-old woman whose hair has gone quite gray in the past year. I've had a fairly stressful year, and since the change in my hair felt quite sudden, I'm wondering if stress could have caused it. If not, what else might be the culprit?

DEAR READER:

It's easy to assume that stress causes gray hair, because there appears to be evidence all around us. Take President Barack Obama as an example.

Compare photos of Obama taken before he ran for president to more recent pictures. You'll notice a distinct difference. His hair used to be consistently dark brown. Now, there are areas of gray dotting the landscape. Is the stress of running a country to blame?

Each hair in your head keeps the color it has. If a single strand of hair starts out brown (or red or black or blond), it is never going to turn gray. If a hair is not gray, no amount of stress can turn that hair gray. If you have a head of brown hair, and then experience the greatest possible stress, your brown hair won't turn gray just like that.

But stress definitely can affect your hair color. It does so by influencing the color of new hairs. Each hair is produced by a single hair follicle. Hairs on the scalp typically live two to five years. When a person's old brown hair dies, the hair follicle that produced the old hair now starts producing a new hair. After we reach age 35, the new hairs produced by a hair follicle tend to lose color, in comparison to the last hair produced by that follicle.

How does stress affect hair color? First, by causing hairs to fall out -- to die young. Stress can cause hair to shed at about three times the rate it normally does. The hair grows back, so the condition doesn't cause balding. But if you're middle-aged and your hair is falling out and regenerating more quickly because of stress, it's possible that the hair that grows in will be gray instead of its original color.

For example, it seems to me that our last two presidents have turned gray pretty fast, maybe faster than they would have if they had not shouldered the burdens of the presidency.

Genetics also influences whether and when you turn gray. In fact, it's probably a stronger cause of graying hair than stress. Look at past generations of your family. This will give you a better indication of when or if you'll go gray than your current stress levels.

We have more information on aging in our Special Health Report, "Living Better, Living Longer: The Secrets of Healthy Aging." You can find out more about it at my website.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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