ROLE OF TRANSEPIDERMAL AND TRANSFOLLICULAR ROUTES IN PERCUTANEOUS-ABSORPTION OF STEROIDS - IN-VITRO STUDIES ON HUMAN SKIN

Percutaneous absorption theoretically comprises two components: the tr ansepidermal and the transfollicular routes. The aim of the present wo rk was to confirm this hypothesis in the human skin by comparing the i n vitro percutaneous absorption of four steroids through scar skin wit hout hair follicles and sebaceous glands and through normal adjacent s kin from abdominal or mammary plasties. In all cases, the absorption o f the four steroids was significantly higher in normal skin than in sc ar skin. The cumulative percentages of progesterone and testosterone a fter 8 h of application were, respectively, 3.1- and 2.4-fold higher i n normal skin than in scar skin. After 24 h of application, the cumula tive percentages of estradiol and hydrocortisone were 1.7- and 2.4-fol d higher in normal skin than in scar skin. At the end of the experimen ts, the quantities of drugs remaining in the skin after 8 or 24 h of a pplication were the same in normal skin and in scar skin except for pr ogesterone for which they were 2-fold greater in normal than in scar s kin. In each case, a histological characterization of the scar skin wa s made in comparison with the normal adjacent skin. The main modificat ions observed on scar skin were the following: absence of hair follicl es and sebaceous glands, thinning of the collagenous fibers with paral lel orientation to the dermoepidermal junction and decrease in the num ber or disappearance of the elastic fibers. These experiments confirme d that human skin appendages, hair follicles and sebaceous glands, con stitute a route of penetration for steroids and thus probably for othe r chemicals of similar molecular weight and properties.