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Pathophysiology and causes of hirsutism

Robert L Barbieri, MD
David A Ehrmann, MD
Section Editors
Peter J Snyder, MD
William F Crowley, Jr, MD
Deputy Editor
Kathryn A Martin, MD


Hirsutism, defined as excessive male-pattern hair growth, affects between 5 and 10 percent of women of reproductive age. Hirsutism may be the initial and possibly only sign of androgen excess, the cutaneous manifestations of which may also include acne and male-pattern balding (androgenetic alopecia). The pathophysiology and causes of androgen-mediated hair growth are reviewed here. Evaluation and treatment of hirsutism are discussed separately. (See "Evaluation of premenopausal women with hirsutism" and "Treatment of hirsutism".)


Hair growth cycle — Humans are born with approximately five million hair follicles, and it is estimated that 80,000 to 150,000 of them are located on the scalp. Hair can be categorized as either vellus (fine, soft, and not pigmented) or terminal (long, coarse, and pigmented) [1]. The number of hair follicles does not change over an individual's lifetime, but the follicle size and type of hair can change in response to numerous factors, particularly androgens.

The hair growth cycle is comprised of three phases [2]:

The growth phase (termed anagen), which varies by body area, is approximately four months for facial hair. Therefore, it takes approximately six months to detect the effects of hormonal therapy for facial hirsutism.

The involutional phase (catagen), which lasts two to three weeks.

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Literature review current through: Nov 2017. | This topic last updated: Jun 09, 2017.
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