Hair Loss and Its Causes

What is the normal cycle of hair growth and loss?

At any one time, about 10 percent of the hair on your scalp is in a resting phase. After 2 to 3 months, the resting hair falls out and new hair starts to grow in its place. This growing phase lasts for 2 to 6 years. Each hair grows approximately 1 centimeter per month during this phase. About 90 percent of the hair on your scalp is growing at any one time.

It is normal to shed some hair each day as part of this cycle. However, some people may experience excessive (more than normal) hair loss.

What causes excessive hair loss?

A number of things can cause excessive hair loss. For example, about 3 or 4 months after an illness or a major surgery, you may suddenly lose a large amount of hair. This hair loss is related to the stress of the illness and is temporary.

Hormonal problems may cause hair loss. If your thyroid gland is overactive or underactive, your hair may fall out. This hair loss usually can be helped by treatment of the thyroid disease. Hair loss may occur if male or female hormones, known as androgens and estrogens, are out of balance. Correcting the hormone imbalance may stop your hair loss.

Many women notice hair loss about 3 months after they've had a baby. This loss is also related to hormones. During pregnancy, high levels of certain hormones cause the body to keep hair that would normally fall out. When the hormones return to pre-pregnancy levels, that hair falls out and the normal cycle of growth and loss starts again.

Some medicines can cause hair loss. This type of hair loss improves when you stop taking the medicine. Medicines that can cause hair loss include blood thinners (also called anticoagulants), medicines used for gout, medicines used in chemotherapy to treat cancer, vitamin A (if too much is taken), birth control pills and antidepressants.

Certain infections can cause hair loss. Children may have hair loss caused by a fungal infection of the scalp. The infection is easily treated with antifungal medicines.

Finally, hair loss may occur as part of an underlying disease, such as lupus or diabetes. Since hair loss may be an early sign of a disease, it is important to find the cause so that it can be treated.

Can improper care of my hair cause hair loss?

Yes. If you wear pigtails or cornrows or use tight hair rollers, the pull on your hair can cause a type of hair loss called traction alopecia (say: "al-oh-pee-sha"). If the pulling is stopped before scarring of the scalp develops, your hair will grow back normally. However, scarring can cause permanent hair loss. Hot oil hair treatments or chemicals used in permanents may cause inflammation (swelling) of the hair follicle, which can result in scarring and hair loss.