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Standardization of an in vitro Model for Evaluating the Bioavailability of Topically Applied Compounds on Damaged Skin: Application to Sunscreen Analysis

Background: Information is lacking on the dermal penetration of topically applied formulations on in vitro skin models, under conditions where the stratum corneum (SC) is damaged. Therefore, we have developed a standardized in vitro barrier-disrupted skin model using tape stripping. Methods: Different tape stripping conditions were evaluated using histology, transepidermal water loss, infrared densitometry, and caffeine absorption. Results: The effects of tape stripping were comparable using pig and human skin. Optimized conditions were used to test the effect of SC damage and UV irradiation on the absorption of an UV filter combination present in a sunscreen. The bioavailability of the filters was extremely low regardless of the extent of skin damage, suggesting bioavailability would not be increased if the consumer applied the sunscreen to sun-damaged skin. Conclusion: This standardized in vitro methodology using pig or human skin for damaged skin will add valuable information for the safety assessment of topically applied products.