“…Drugs for topical or systemic treatment of skin diseases are tested in vitro using keratinocyte cultures or in vivo in human beings or in laboratory animals (Wrench, 1981;Marks et al, 1983;Zmolek et al, 1983;Lowe et al, 1984;van den Hoven et al, 1987;Hofbauer et al, 1988;Lubach & Kietzmann, 1988a,b;Kietzmann & Lubach, 1989). Because of differences in the histology and metabolism of the epidermis of different skin regions, the compatibility of results is often poor.…”