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j. Soc. Cosmet. Chem., 37, 249-265 (July/August 1986) The athymic nude mouse grafted with human skin as a model for evaluating the safety and effectiveness of radiolabeled cosmetic ingredients ROBERT V. PETERSEN, Department of Pharmaceutics, College of Pharmacy, Universit 3, of Utah, Salt Lake City, UT 84112,' M. SERPIL KISLALIOGLU, Department of Pharmaceutics, College of Pharmacy, Idaho State University, Pocatello, ID 83209,' WEN-QUAN LIANG, and SEN-MAW FANG, Department of Pharmaceutics, College of Pharmacy, University of Utah, Salt Lake City, UT 84112,' MONSOOR EMAM, Division of Dermatology, College of Medicine, University of Utah, Salt Lake City, UT 84112,' and STEVEN DICKMAN, Microbiological Development and Control, Inc., 520 Wakara Way, University of Utah Research Park, Salt Lake City, UT 84108. Received July 30, 1984. Presented at the Annual Scientific Meeting of the Society of Cosmetic Chemists, New York. December 1-2, 1983. Synopsis The safety and efficacy of cosmetic ingredients have been major concerns for the cosmetic chemist for many years. However, most animal models currently used to evaluate the safety of various topically-applied substances do not provide data which can readily be correlated with anticipated human responses to these substances. Recent studies have demonstrated clearly that a wide variety of chemical agents have the ability to penetrate the skin and even to enter the systemic circulation. Many researchers are studying a number of drugs as potential candidates for use in transdermal delivery systems. It has been shown that some cosmetic ingre- dients may also permeate the skin to varying degrees. This report describes a new technique for deter- mining the extent of penetration of radiolabeled agents into the stratum corneum and underlying tissues. The technique utilizes human skin which has been grafted onto the athymic nude mouse. Penetration of various labeled materials is determined either by tape-stripping the skin and counting radioactivity using a scintillation counter or by obtaining punch biopsies of the grafted skin followed by rapid freezing, cryo- stating, and autoradiography of the biopsied skin tissues. Components of the Natural Moisturizing Factor (NMF) were used in these studies. These and other studies show conclusively that various amino acids, urea, lactic acid, p-aminobenzoic acid, and other agents penetrate into and through the stratum corneum of the grafted human skin to varying degrees. This model likely approximates natural human cutaneous absorption characteristics better than any other non-human model commonly used today. INTRODUCTION Human skin, once considered to be an impervious barrier which protects the body from 249