j. $oc. Cosmet. Chem., 34, 317-326 (September/October 1983) The use of the domestic pig as an animal model of human dry skin and for comparison of dry and normal skin properties DONALD L. BISSETT and JAMES F. McBRIDE, The Procter & Gamble Company, Miami Valley Laboratories, Cincinnati, OH 45247. Received February 1, 1983. Presented at the Society of Cosmetic Chemists Annual Scientific Seminar, Cincinnati, Ohio, May 1983. Synopsis At low relative humidity, the domestic pig develops dry, scaly skin on its dorsum. This dry skin is visually like that seen on humans, and responds to treatment with known skin conditioners. This animal model is valuable as a tool for screening skin conditioning materials and comparing the properties of dry and normal skins. Comparison of dry and normal dorsal pig skins revealed no differences in stratum corneum thickness, turnover rate, water-binding capacity, or "natural moisturizing factor" (NMF) content. Dry skin did have an increased nonpolar lipid content. This lipid was confined to the upper stratum corneum and was sebaceous in origin. Dry skin in the pig appears to be a phenomenon of the upper stratum corneum. INTRODUCTION The importance of water in skin conditioning was first reported by Blank in 1952 (1). He observed that applied oils did not soften dehydrated stratum corneum (callus), but that water was readily absorbed by the tissue and softened it, indicating that the water content of stratum corneum was of great importance in maintaining flexibility and, presumably, good skin condition. It is generally accepted that dry skin has a reduced water content. However, there is no generally accepted model of the properties of dry skin. Most determinations have been done using abnormal tissue, such as callus (1), or diseased skin, such as that present in ichthyosis, psoriasis, and essential-fatty-acid deficiency (2-6). These tissues were used because of the lack of dry skin for in vitro research and because of their visual similarity to dry skin. The results from use of these abnormal tissues predict that dry skin is thickened, is hyperproliferative, is depleted in "natural moisturizing factor" (NMF) (7), is deficient in water-binding capacity, has an abnormal lipid composition, and has an abnormal permeability to water. The lack of an animal model for dry skin has been a barrier to progress in this area. We report here the development of an animal model of dry skin and some of the properties of that dry skin. 317