J. Soc. Cosmet. Chem. 25 381-395 (1974) ¸ 1974 Society of Cosmetic Chemists of Great Britain Sex hormones and skin F. J. EBLING* The 1974 Medal Lecture by Professor F. J. Ebling, Department of Zoology, University of Sheffield, Sheffield SlO 2TN, delivered before the Society of Cosmetic Chemists of Great Britain on the 7th March 1974 with G. A. C. Pitt Esq., President of the Society in the Chair. Synopsis---As well as its more obvious ANATOMICAL and PHYSIOLOGICAL functions the SKIN plays an important part in social communication by vision, touch and smell. The epider- mal surface, the activity of the glands and the distribution of the HAIR are particular features of skin which are concerned with sexual communication, and it is thus not surprising that they are profoundly influenced by HORMONES. STEROIDS have been widely used in efforts to improve skin texture the effect of OESTROGENS is equivocal, but ANDROGENS certainly stimulate epidermal cell division. The SEBACEOUS GLANDS are unequivocally stimulated by androgens and inhibited both by oestrogens and anti-androgenic steroids, though their modes of action are not identical. PITUITARY factors appear to be necessary, at least in the rat, for the response of the sebaceous glands to TESTOSTERONE, and it seems possible they may act upon the conversion of the steroid to its active metabolites. Human body, AX1LLARY and pubic hair is similarly androgen dependent. So sebum secretion, the growth of sexual hair, and hirsutism may be inter-related by their link with steroid metabolism within the skin. Is it possible that one function, or at least one by-product, of cutaneous androgen metabolism is the manufacture of pheromones or odours? INTRODUCTION When the human skin is viewed against its evolutionary inheritance, certain features are clear. We do not question its functions as a sensory structure or as a defensive barrier against both physical injury and chemical assault. Its role in preventing loss of precious water has been part of verte- brate history ever since some distant amphibious ancestor took the first steps to emerge from a primaeval swamp. * Department of Zoology, The University, Sheffield S10 2TN. 381

382 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The evolution of warm blood-bloodedness in the mammals was accom- panied by the development of an insulating material known as hair. To adjust the pelt at intervals to seasonal changes in temperature, hair follicles undergo cycles of activity which appear to be linked to environmental changes through the endocrine system even the human hair may retain a remnant of this moult cycle. But men were enabled to leave the forests and fan out through new fields by the development of superb mechanisms for keeping cool. Hair was lost, its insulating qualities being to some extent replaced by fat the vascularity of skin became greatly increased, though heat loss could be reduced by shunting the blood through the deeper layers and eccrine glands which could be brought into play for cooling developed over virtually the whole surface of the body. The first men were almost certainly dark skinned as the body hair became reduced, melanin pigmentation provided a protection against the damaging effects of ultraviolet radiation. But as man moved into areas where even the summer sun moved low in the sky the threat of radiation damage was replaced by another, namely the failure to synthesize vitamin D. So natural selection switched to favour pale skin. The evolutionary legacy is still reflected by the fact that Europeans tend to develop skin cancer in the tropics and West Indian immigrants to get rickets in Great Britain. Our thinking about skin tends to be dominated by these evolutionary facts which concern our biological survival as individuals. But there is another level at which natural selection has operated, namely that of the social group. The survival of the group depends upon its coherence by communication, between the sexes, as Darwin himself realized, in the family, and throughout the troop. Although overshadowed by the sophisticated use of language, and sometimes suppressed because of its embarrassing inevitability, the role of skin remains important. Much of the behaviour of our vertebrate ancestors was innate, that is to say it was programmed by heredity patterns of courtship or aggression in one individual were automatically set in motion by so-called releasing mechanisms--physical structures, colours, movements, scents or sounds-- in another. While mammalian and particularly human social interactions have become increasingly dependent on learned and thus much more rapidly modifiable patterns, the releasing features are still present, and more than a remnant of the innate responses still remains. The buttocks provide a good fundamental example of a visual releaser. When a female ape is sexually receptive, they become red and swollen and she displays them to attract the male. In man they become permanently