Alopecia-hair loss or baldness-affects some 30 million women in the United States, young and old, according to the American Academy of Dermatology. But hair loss in women is different from male pattern baldness (androgenic alopecia). For years, scientists believed that the same process was at work in female pattern baldness as in the male version-a genetically inherited sensitivity to dihydrotestosterone, a by-product of testosterone that can accumulate in and damage the hair follicle. But today, we know that baldness in women can be the result of many factors-there may be a variety of other types of enzymes, as well as hormone receptors and blockers at work.

Hormonal changes following menopause (including changes in the levels of androgens) can produce “female pattern baldness.” Whereas male pattern baldness usually starts at the temple area or the crown (that bald spot in the back), women more typically have a diffuse thinning around the whole top of the head, with the frontal hairline maintained. But remember-young women, as well as postmenopausal women, can experience hair loss. Other factors in female alopecia can include hormonal changes following pregnancy, and polycystic ovary syndrome (a fairly common hormonal problem in women). There’s also alopecia areata-patchy areas of total hair loss caused by an immune disorder-and telogen effluvium-a temporary shedding of hair following childbirth, crash dieting, or surgery. Certain kinds of prescription drugs and chemotherapies can also cause hair loss. There are many possibilities. So the first thing a woman should do if she notices that she’s losing hair is to see her doctor and get to the-excuse the pun-root cause.

A lesser known cause of baldness in women is something called trichotillomania (TTM), which is defined, in the venerable Diagnostic and Statistical Manual of Mental Disorders, as “the recurrent pulling out of one’s hair that results in noticeable hair loss.” (Trichotillomania is classified by some clinicians as a form of obsessive-compulsive disorder.) Among adults, TTM is more common among females than among males. A practice related to TTM is called trichophagia, in which the hair is sucked or eaten. And on the most exotic end of the hair-yanking spectrum is Rapunzel syndrome, in which people who eat their hair develop a small or large bowel obstruction caused by a trichobezoar… yes, you guessed it-a hairball.