The normal cycle of hair growth lasts for 2 to 6 years. Each hair grows approximately 1 centimeter (less than half an inch) per month during this phase. About 90 percent of the hair on your scalp is growing at any one time. About 10 percent of the hair on your scalp, at any one time, is in a resting phase. After 2 to 3 months, the resting hair falls out and new hair starts to grow in its place. 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. Hair loss of this type can affect men, women and children.

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 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. Fungal infections of the scalp can cause hair loss in children. 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.

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 (also called "perms") may cause inflammation (swelling) of the hair follicle, which can result in scarring and hair loss.

The term "common baldness" usually means male-pattern baldness, or permanent-pattern baldness. Male-pattern baldness is the most common cause of hair loss in men. Men who have this type of hair loss usually have inherited the trait. Men who start losing their hair at an early age tend to develop more extensive baldness. In male-pattern baldness, hair loss typically results in a receding hair line and baldness on the top of the head. Women may develop female-pattern baldness. In this form of hair loss, the hair can become thin over the entire scalp.

Perhaps. Your doctor will probably ask you some questions about your diet, any medicines you're taking, whether you've had a recent illness and how you take care of your hair. If you're a woman, your doctor may ask questions about your menstrual cycle, pregnancies and menopause. Your doctor may want to do a physical exam to look for other causes of hair loss. Finally, blood tests or a biopsy (taking a small sample of cells to examine under a microscope) of your scalp may be needed.

Depending on your type of hair loss, treatments are available. If a medicine is causing your hair loss, your doctor may be able to prescribe a different medicine. Recognizing and treating an infection may help stop the hair loss. Correcting a hormone imbalance may prevent further hair loss. Medicines may also help slow or prevent the development of common baldness. One medicine, minoxidil (brand name: Rogaine), is available without a prescription. It is applied to the scalp. Both men and women can use it. Another medicine, finasteride (brand name: Propecia) is available with a prescription. It comes in pills and is only for men. It may take up to 6 months before you can tell if one of these medicines is working. If adequate treatment is not available for your type of hair loss, you may consider trying different hairstyles or wigs, hairpieces, hair weaves or artificial hair replacement.