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j. Soc. Cosmet. Chem., 39, 15-26 (January/February 1988) Relationship between skin permeability and corneocyte size according to anatomic site, age, and sex in man ANDRI• ROUGIER, CLAIRE LOTTE, PIERRE CORCUFF, and HOWARD I. MAIBACH, Dgpartement de Biologie (A.R., C.L. ) and Dgpartement de Biophysique ( P. C. ), Laboratoires de Recherche Fondamentale de l'Orgal, I Avenue Eugene Schueller, 93600 Aulnay sous Bois, France, and Department of Dermatology, University of Cali•brnia, San Francisco, CA 94143 (H.I.M.). Received July 8, 1987. Synopsis Postauricular and forehead stratum corneum (SC) exhibit greater permeability ehan SC of the arm, the forearm, or the abdomen. This greater permeability seems to correlate with smaller corneocyte area. The permeation of benzoic acid through arm SC of aged persons (65 to 80 years) appears reduced when compared with permeation through arm SC of younger persons. However, the permeability of water through the same membrane, measured by transepidermal water loss, does not seem to be affected by aging. INTRODUCTION In its role as barrier, the skin participates in homeostasis by limiting the inward move- ment of environmental agents and by limiting the water loss. Transepidermal water loss (TEWL) (1,2) and percutaneous absorption (3,4) are parameters related to the func- tional state of the cutaneous barrier. Apart from pathologic considerations, this func- tional state may vary considerably under physiologic conditions (1). Thus, in man, cutaneous permeability to both water and applied compounds varies according to ana- romic site (2-6). During the past two decades several functions of the stratum comeurn have been docu- menrated. However, despite the efforts of dermatologists and cosmetic scientists the stratum corneum has not yet revealed much information about its structure-function relationships. Corneocytes differ markedly from the keratinocytes that produce them. The most ob- vious difference is the disc-like shape of the corneocytes, allowing them to present a large surface area in the horizontal dimension. The surface area of corneocytes is not constant thus there exist site (7) and age (8- 10) differences. This suggests that studies 15