A HAIRLESS MOUSE MODEL FOR ASSESSING THE CHRONIC TOXICITY OF TOPICALLY APPLIED CHEMICALS

An enormous number of synthetic chemicals are incorporated in topical drugs, cosmetics and toiletries. These have the potential to cause irr itant reactions when chronically applied to human skin. In predictive tests for assessing the irritancy potential of these chemicals, haired species, especially rabbits, guinea pigs and mice, have figured promi nently. Customarily these tests, including the renowned Draize rabbit test, have entailed a single acute exposure or at most daily exposures over a few weeks. Estimation of inflammation and tissue injury in the se models have relied on visual assessment. We submit that this approa ch is no longer acceptable. Visual assessments are unreliable. Reactio ns which are scored equivalently by the naked eye may differ strikingl y when examined histologically. Moreover, tissue injury may be present in clinically normal skin. Short-term results, even when abetted by r outine histological evaluations, cannot predict the degree of injury f rom longterm exposures. Cosmetics and toiletries, for example, are use d daily for decades, often over most of the lifespan of persons who ar e well groomed. We present the hairless mouse as a convenient, reliabl e model for assessing the chronic toxicity of diverse chemicals. Histo logical examination enables a detailed description of the different ti ssue components which participate in the complex cascade of changes th at comprise the inflammatory response. (C) 1998 Elsevier Science Ltd. All rights reserved.