Definition and causes of hirsutism

Hirsutism is defined as excessive terminal hair in females (in this topic, female is used to mean anyone presumed female at birth) that is distributed in a male pattern. Terminal hair is coarse and pigmented, unlike vellus hair, which is fine, soft and relatively unpigmented. In hirsutism, androgens induce vellus follicles in sex-specific areas of the body to develop into terminal hairs. Hirsutism may affect only one region (eg lower face) or may be widespread (eg including limbs, chest, and midline of trunk).

Hirsutism should be differentiated from hypertrichosis, a widespread overgrowth of non–androgen-dependent hair in areas like the forehead and forearms. Occasionally, hypertrichosis is an adverse effect of drugs (eg ciclosporin, minoxidil, penicillamine, phenytoin).

Hirsutism results from:

• androgen excess of ovarian origin (biochemical hyperandrogenism caused by polycystic ovarian syndrome) in 70 to 80% of cases
• an increased responsiveness of the hair follicles to normal circulating androgens (idiopathic hirsutism) in 5 to 20% of cases.

Less common causes of hirsutism include:

• nonclassical congenital adrenal hyperplasia
• androgen-secreting tumours of the ovaries or adrenal glands
• Cushing syndrome
• exogenous corticosteroids or accidental transfer of topical testosterone from a partner
• sodium valproate therapy.