As I approach 40, it seems my hair is thinning rapidly. Are there possible medical reasons why a woman of my age might be losing hair? How can I find out if I'm likely to suffer this fate?

For a look into what your future holds, start by digging out a family album. Thinning hair (like hair color) is a familial trait. If your mother and grandmother lost their hair, you probably will too. If you think you're losing your hair prematurely, there may be several possible medical explanations.

Thyroid disease can cause thinning hair. All women should be periodically screened for thyroid problems with a blood test. If testing shows a thyroid problem, then appropriate medical treatment is important for your overall health as well as the health of your hair.

Some thinning of hair can be attributed to stress. Hair is constantly growing and being shed--on average, we lose up to 100 hairs a day! A traumatic event or an illness can disrupt this cycle of hair growth and loss causing a lot of hairs to fall out at once, instead of a few hairs falling out every day. Hormonal factors like pregnancy and menopause can also rearrange the hair growth/hair loss cycle.

Some dermatological conditions and infections can cause hair loss as well. If your scalp seems red or itchy or unusually flaky, or if you have small but distinct bald patches, a visit to a dermatologist is in order. And don't forget the things we do to our hair -- teasing, pulling it into a tight ponytail, perming and coloring; all of these can lead to increased hair loss.

So where do you go from here? I'd suggest you talk with your doctor about your hair loss and any other symptoms you may be noticing. A complete physical, including thyroid tests, may be in order. The good news is that most causes of hair loss can be treated.