Hair: The Long and Short of It

Some hair on your head falls out every day, no matter what your age. And that is perfectly normal.

Each hair strand goes through two phases: a growing phase and a resting phase, according to the American Academy of Family Physicians (AAFP). The growing phase lasts two to six years, during which the strand grows about half an inch a month. When the growing phase ends, the hair enters a resting phase of two to three months. After the resting phase, the hair falls out and a new hair begins growing.

About 10 percent of your hair is in a resting phase at any one time, the AAFP says.

About 95 percent of all cases of excessive hair loss are caused by male pattern baldness, according to the American Medical Association (AMA). This condition, technically called androgenetic alopecia, occurs most often in men, but women also can experience it. About 40 million U.S. men are affected by male pattern baldness. About a quarter of men begin balding by age 30, the AMA says. Two-thirds of men begin balding by age 60.

Excessive hair loss can be caused by other things, as well. You can lose hair three to four months after an illness or surgery, because of the stress on your body. A hormonal imbalance -- caused by thyroid disease, for instance -- can cause hair loss. Women often notice hair loss about three months after giving birth; this hair loss is related to levels of certain pregnancy hormones.

Other causes

• Fungal infections can cause hair loss. These infections occur most often in children. Treating the infection stops the hair loss.

• Certain medications can cause hair loss. These include blood thinners, gout medicines, chemotherapy medicines, oral contraceptives and antidepressants, the AAFP says. An excess amount of vitamin A also can cause hair loss.

• Diabetes and lupus are two diseases that can cause hair loss. Treating the disease can help stop the hair loss, the AAFP says.

• Using tight hair rollers or wearing your hair in pigtails or cornrows can lead to hair loss. Chemicals used in permanents also can lead to hair loss.

If you have male pattern baldness, be wary of miracle cures. The good news is that there is hope: medications such as minoxidil, which is applied topically, or finasteride taken as a pill, can help restore hair growth, and techniques such as hair grafts or transplants can be successful.

Proper care can keep hair healthy. The difference in shampoos for oily, dry and normal hair depends on pH balance -- whether they're acidic or alkaline. Dry or damaged hair, for example, needs acidic shampoo, with a pH below five.

And if you have trouble making your hair look lively, maybe you should not be surprised. Your hair is made up of layers of dead cells filled with the protein keratin -- which also makes up your nails and your outer skin.