Hair Loss

Androgens play a pivotal role in the growth of pubic and axillary hair. Androgens stimulate growth of beard hair, whereas in the scalp, androgens inhibit hair regrowth. Clinical studies by James B. Hamilton in the early 1940's suggested that the balding process is promoted by androgens in genetically predisposed men, referred to as androgenetic alopecia or male pattern hair loss. The androgen acting in the scalp to promote the balding process was not known at the time. It was not until the 1960's when it was discovered that testosterone is converted to the more bioactive androgen dihydrotestosterone by the microsomal, NADPH-dependent enzyme steroid 5alpha-reductase in peripheral androgen-responsive tissues such as the prostate and skin [4]. Two genes encoding two isoenzymes of steroid 5alpha-reductase exist, designated type 1 and type 2 [5, 6]. The type 1 isoenzyme is the major 5alpha-reductase in skin, has a neutral pH optimum and a low affinity for testosterone. Steroid 5alpha-reductase type 2, on the other hand, is the major isoenzyme in the prostate, has an acidic pH optimum and a high affinity for testosterone. The notion that DHT, and not testosterone, is the androgen responsible for benign prostate hyperplasia and male pattern hair loss stems from the observation that men with steroid 5-alpha-reductase 2 deficiency present with a hypoplastic prostate and do not develop male pattern baldness . Consequently, the 5 alpha-reductase type 2 isoenzyme-specific inhibitor finasteride has proven efficacious in promoting hair regrowth as a consequence of lowering scalp and plasma DHT levels, and in the treatment of benign prostate hyperplasia by lowering prostatic DHT.