Androgenetic alopecia is characterised by progressive, patterned hair loss from the scalp. Recently the pathogenesis and genetic basis of the hair loss have been better understood, as has the distress experienced by men who have lost their hair. There have also been breakthroughs in the treatment of androgenetic alopecia.

The transition of some terminal hairs into vellus hairs is a universal physiological secondary sexual characteristic.1 Androgenetic alopecia becomes a medical problem only when the hair loss is subjectively seen as excessive, premature, and distressing.

The prerequisites for premature androgenetic alopecia are a genetic predisposition and sufficient circulating androgens.2 Eunuchs do not go bald.3 Every white man possesses the autosomal inherited predisposition,4 and 96% lose hair to some degree,5 but because of the variabity of gene expression far fewer have appreciable premature hair loss.