The androgen-sensitive skin appendages (sweat gland, hair follicle, and sebaceous gland) each metabolize androgens in a characteristic pattern; however, sweat glands and sebaceous glands account for the vast majority of androgen metabolism in skin (Table 1) (105, 106, 107, 108). 3ß-Hydroxysteroid dehydrogenase (HSD) is particularly prominent in sebaceous glands (109, 110). Type 2 17ß-HSD mRNA expression has been reported in outer root sheath cells of cultured human hair, and type 3 17ß-HSD expression in beard and axillary dermal papilla cells from both sexes (111). The former favors inactivation of estrogen; the latter favors formation of testosterone. The predominant 17ß-HSD isozyme expressed in human sebaceous glands at both the mRNA and protein level is the type 2 form (112). Furthermore, the oxidative activity (conversion of estrogen and testosterone to less active precursors) of 17ß-HSD is greater in sebaceous glands from non-acne-prone skin as compared with acne-prone regions. A predominance of 5-alpha-reductase over 17ß-HSD activity appears to favor DHT formation in sweat glands and in the outer root sheath cells of pubic, as compared with scalp, hairs. In addition, 5-alpha-reductase is 2 to 4 times more active than 17ß-HSD in sebaceous glands from facial skin (113). A summary of the localization of the mediators of androgen signal transduction in the PSU is provided in Table 2.