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j. Soc. Cosmet. Chem., 46, 291-299 (November/December 1995) A comparison of three in vitro screening tests with an in vivo clinical test to evaluate the irritation potential of antibacterial liquid soaps BOYCE M. MORRISON, JR., and MARC PAYE, Colgate-Palmolive Company, 909 River Road, Piscataway, NJ 08855 (B. M. M. ), and Colgate-Palmolive Research & Development, Liege, Belgium (M.P.). Received July I, I994. Presented at the 18th IFSCC Congress, Venice, Italy, October I994. Synopsis A series of in vitro screening studies has been performed to determine the irritation potential of antibacterial liquid soaps. The results from these in vitro studies were compared to the results from an in vivo clinical study in an effort to determine their utility. Three in vitro techniques were employed to evaluate antibacterial liquid soaps: the collagen swelling test, the pH rise test, and the zein test. In order to compare the data from these three tests, a solution of 1% SLS was included as a positive control. This enabled the data for the antibacterial liquid soaps to be expressed as a percentage of the SLS score. The in vivo clinical test was the modified soap chamber test. The skin was evaluated for irritation using clinical parameters (such as erythema) and biophysical techniques (evaporimetry and chromametry), and the data from the test products were normalized to the data of a mild control product. The overall ranking of the antibacterial liquid soaps from the soap chamber test had a good correlation with the ranking from the collagen swelling test (r = 0.71) and the pH rise test (r = 0.81). The correlation with the zein test was not as good (r = -0.26). However, if the data from the three tests were averaged, the best correlation was achieved with the in vivo results (r = 0.94). In conclusion, each of these tests was used to predict product-induced irritation to the skin. These tests were used individually and collectively. The best correlation occurred when the antibacterial liquid soaps were ranked according to their total in vitro score and compared with the in vivo ranking. INTRODUCTION In vitro assays have been developed to predict the skin's response to surfactant-induced irritation (1-7). These assays are quite useful when a large number of surfactants need to be screened for their irritation potential. Three of these tests, collagen swelling, pH rise, and the zein test, had previously been evaluated by our group to determine their ability to predict surfactant-induced erythema from single-surfactant systems (8). The results showed that each of the methods was based on a similar principle of protein 291