normally hair goes through a regular growth cycle. during the anagen phase which lasts three to four years the hair grows. during the telogen phase which lasts about three months the hair rests. at the end of the telogen phase the hair falls out and is replaced by new hair. the average person loses about 100 hairs each day. losing excess hair can be a normal part of growing older but it also can have other causes including drugs or disease. as they age men tend to lose the hair on top of their head which eventually leaves a horseshoe-shaped ring of hair around the sides. this type of hair loss is called male-pattern baldness. it's caused by genes (from both parents -- the idea that men take after their mother's father is a myth) and it's fueled by the male hormone testosterone. in female-pattern baldness the hair loss is different -- it thins throughout the top of the scalp leaving the hair in front intact. a number of disorders can cause the hair to fall out. people who have an autoimmune condition called alopecia areata lose hair on their scalp as well as on other parts of their body. other health conditions that can cause excess hair loss include: medications such as antidepressants retinoids nsaids blood thinners birth control pills and other hormonal treatments high blood pressure medications chemotherapy and radiation severe infections major surgery overactive or underactive thyroid other hormonal problems severe stress autoimmune diseases such as lupus fungal infections of the scalp pregnancy and childbirth certain hair care practices such as wearing tight ponytails or weaves or regularly bleaching or perming the hair can also lead to hair loss. some people compulsively pull out their hair. this psychological disorder is called trichotillomania. when hair loss is related to a medication stopping the drug usually prevents further hair loss and the hair will eventually grow back. hair also tends to grow back after most illnesses radiation therapy or chemotherapy. wearing a wig or hat can hide the hair loss until the hair returns. hair transplants are a more permanent hair-replacement solution. hair lost to male-pattern and female-pattern baldness won't grow back on its own but there are medications that can help slow hair loss and even regrow hair. minoxidil (rogaine) is a cream that is available over the counter to treat men and women. finasteride (propecia) is a pill that is available to men only by prescription. topical or injectable cortisone may also help regrow hair lost to certain conditions.
what causes hair loss?