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j. Soc. Cosmet. Chem., 41, 249-257 (July/August) ImmunologyConcepts and skin relationships GEOFFREY BROOKS, Brooks Industries, South Plainfield, NJ, and BERNARD IDSON, Austin, TX 78759. Synopsis The classical concept of the function of skin as a barrier versus the environment is being expanded with the recognition that important metabolic and immunologic processes also occur. The immunological role of skin has been expanded from a simple target of immune injury to an active role in the initiation and regulation of certain skin-associated immune responses. This review presents the fundamentals of mecha- nisms underlying the skin immune system. Included are discussions of antigens, antibodies, allergens, lymphocytes, compliment, macrophages, Langerhans cells, keratinocytes, and interleukins, as well as the roles of antioxidants, UV light, and fatty acids. INTRODUCTION Concepts of the function of skin have changed in the last decade from that of a barrier against microbiologic and chemical invasion to include an important role in immunity. There is increasing recognition that skin could serve as a target organ of immunologic injury and in the initiation and regulation of both local and systemic immune respon- siveness (1). Immunodermatology is primarily directed toward an understanding of immunological mechanisms operating in skin as a complementary line of defense against external assault (2). Classical concepts of the function of skin have focused primarily on its capacity to establish and maintain an effective barrier versus the environment. Stratum corneum, the outermost region of the skin, serves as the most important component of the barrier. Within the last several decades, the barrier concept of epidermal function has been expanded with the recognition that important metabolic and immunologic processes also occur at this interface. Investigators from the clinical and basic sciences first studied the biochemical features of skin, with primary attention to the factors that regulate the function of skin cells such as keratinocytes, melanocytes, and fibroblasts. Other investigators collected data that suggested that many skin disorders possessed features of immunologic relevance. More recently the immunologic role of skin has been expanded from a simple target of immune injury to an active role during the initiation and regulation of certain skin-associated immune responses (3). This review is intended to acquaint cosmetic scientists with the fundamentals of the complex mechanisms underlying the skin immune system (SIS). 249