At puberty, when their testes begin secreting significant quantities of male sex hormones (androgen), males develop the typical male pattern of hair growth, including a beard and a hairy chest. In females, both the ovaries and the adrenal glands produce small quantities of androgen.
Occasionally, a tumor of one of these glands over secretes androgen and causes hirsutism. This is a condition of excessive hairiness of the upper lip, chin, chest, inner thighs and abdomen in females of prepubertal males.
Surprisingly, androgen also must be present for the most common form of baldness, male-pattern baldness, to occur. In genetically predisposed males, androgen somehow inhibit hair growth.
In 1979 a report noted that a new blood pressure medicine had the side effect of causing hair growth. The result was an immediate stampede to test its effectiveness in treating baldness.
The drug is minoxidil (Rogaine) a potent vasodilator, that is, a drug that widens blood vessels and increases circulation. When applied topically, it does stimulate some hair regrowth in some persons with thinning hair due to male-pattern baldness.
For many, however the hair growth is meager, and it does not help individuals who already are bald.
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