No one wants to see a clump of hair in the bathtub drain, but excessive hair loss can be especially distressing for women. When a woman's hair becomes noticeably sparse, the cause is usually a derivative of the male hormone testosterone called dihydrotesterone (DHT). Although DHT is the cause of male pattern baldness, it is also responsible for excessive hair loss in women.
Normal Growth Cycle
Hair normally goes through periods of growth and shedding, according to the Mayo Clinic. The hair grows during the anagen phase, which lasts two to three years, then enters a brief resting period. After resting for three to four months, the hair falls out and the process starts again with a new hair. Hair loss is a normal part of the hair cycle, and people can lose up to 100 strands of hair daily with no noticeable effect. Shedding becomes a problem only when the hair loss outpaces the new growth.
Androgenetic Alopecia
Androgenetic alopecia, or pattern baldness, is the leading cause of hair loss in women, says Paul McAndrews, M.D., of the American Hair Loss Association. Androgenetic alopecia may cause different patterns of hair loss in women than in men. In men, baldness typically occurs in distinct patterns, whereas in women, the hair loss tends to be scattered all over the scalp, resulting in widespread thinning and baldness.
Hormones and Hair Loss
An enzyme in the oil glands of the hair follicles converts testosterone to DHT. DHT reduces the size of the hair follicles to the point where healthy hair can no longer survive, says McAndrews. The level of DHT is important to hair loss, not the amount of circulating testosterone. Even though women produce testosterone in much smaller quantities than men, low levels of the hormone can still be converted to DHT. DHT levels typically fluctuate, explains McAndrews, but levels within the normal range may lead to hair loss if the individual is genetically sensitive to the effects of DHT.
Causes of Hormonal Imbalances
Several factors other than heredity may disrupt the hormonal balance between testosterone and estrogen, leading to androgenetic alopecia, states McAndrews. During menopause, estrogen production almost ceases, disrupting the balance of male and female hormones. Estrogen levels are also affected by pregnancy, oral contraceptive use, underactive thyroid and ovarian cysts.
Other Common Causes
Traumatic events may also cause hair loss in women, says McAndrews, by forcing hair prematurely into the shedding phase. Beginning three to six weeks after the event, hair that should be in the growing or resting phase may fall out. Childbirth, major surgery, serious illness or infection, extreme stress or malnutrition may cause excessive hair loss. In most cases, hair growth resumes when the traumatic event resolves.
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