BIOCHEMICAL-MECHANISMS REGULATING HUMAN HAIR-GROWTH

The human hair follicle cycles in active growth and resting phases con trolled by a complex network of biochemical processes, yet to be fully understood. It is well known that hair follicles on scalp respond to androgens by a shortening of the anagen growth phase causing hairs to regress to a finer, thinner texture. The target tissue androgens, test osterone, and dihydrotestosterone can circulate systemically to skin o r can be formed locally in hair follicles and sebaceous glands by spec ific enzymes in the steroid cascade. Kinetic constants have been evalu ated for several enzymes which mediate dihydrotestosterone formation, including 5a-reductase, and the cytochrome P-450 aromatase enzyme in i solated human hair follicles and sebaceous glands from scalp of men an d women with androgenetic alopecia. The levels of these enzymes differ ed between men and women, and from frontal versus occipital sites with in the same patient, indicating that similar steroid mechanisms may be taking place in men and women, but the amount or level of enzymes var y, perhaps explaining why men have more severe patterns of hair loss t han women. Knowing the differences between men and women with androgen etic alopecia could shape more effective treatment options in the futu re.