Numerous factors of intrinsic or extrinsic origin may influence growth of hair in normal persons. Genetic factors are the most important, but their inheritance is complex and little understood. Considerable overlap is observed between normal men and women in the amounts and distribution of terminal hair, the main differences being quantitative rather than qualitative. The endocrine control of growth of hair is effected through the secretion of androgens, especially testosterone, which is the principal stimulus for its growth. However, the ability to respond is an intrinsic quality unique to the hair follicle itself.
Increased hairiness asserts itself in many normal situations such as adolescent development, pregnancy and menopause, as well as in premature pubarche and precocious puberty. The degree and extent of hirsutism in these conditions will be predicated, for the most part, by inheritance.
It is extremely difficult to influence growth of hair locally by direct stimulation of the skin. Only repeated cutaneous stimuli applied over a prolonged time, such as is seen in emotionally disturbed patients who repeatedly bite their skin, will increase the growth of terminal hair significantly.
Drug-induced hirsutism is an increasingly frequent complication. Dilantin ®, diazoxide, ACTH and corticosteroids, and hexachlorobenzene produce hirsutism without significant masculinizing side effects. Steroidal compounds, such as progestogens and anabolic steroids, are potentially androgenic and may produce hirsutism, although the incidence is probably low and dependent on individual susceptibilities. Testosterone used in the treatment of diseases such as cancer or endometriosis would be expected to cause significant masculinizing side effects; the degree of hirsutism varies considerably among women using similar amounts of the drug.
Endocrinologic abnormalities affecting the pituitary gland, adrenal glands or ovaries cause hirsutism in approximately 1 per cent of women who complain of excessive hair. An endocrinologic abnormality is much more likely in severely affected patients, especially when signs of defeminization or masculinization are present. The most commonly associated