296 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 6• 2• r = -0.26 p = 0.57 0 1 2 3 4 5 6 7 In Vitro Ranking Figure 4. Correlation between the ranking of antibacterial liquid soaps using the zein test and the ranking of antibacterial liquid soaps using the modified soap chamber test. rinsed with running tap water and patted dry. The panelists waited three hours before skin irritation assessments of redness (clinical and instrumental, using the Minolta Chroma Meter) and barrier damage (Servo Med Evaporimeter). The products were reapplied for a further 21 hours and assessed as above, as well as 24 hours after patch removal. The products were ranked on their overall irritation score based on their propensity to produce erythema and skin barrier damage. RESULTS IN VITRO RESULTS Table II summarizes the results of the three in vitro studies. In order to compare the irritation prediction scores for the three methods, the results have been expressed as a percentage of the score obtained with a solution of SLS at 1% in each of the tests. There is some variation as to how the three tests rank the products. The collagen swelling test ranks Product B as the mildest and Product F as the most irritating. The pH rise test

EVALUATING IRRITATION POTENTIAL 297 I ß r = 0.94 p = 0.035 0 I 2 3 4 5 6 7 Overall In Vitro Ranking Figure 5. Correlation between the ranking of antibacterial liquid soaps using all three in vitro tests and the ranking of antibacterial liquid soaps using the modified soap chamber test. ranks Product A as the mildest and Product F as the most irritating. The zein test, on the other hand, ranks Product F as the mildest and Product E as the most irritating. Summing the scores from the three tests predicts Product B to be the mildest and Product F the most irritating. IN VIVO RESULTS The data from the soap chamber study are summarized in Table III. The clinical scores for erythema and the changes in skin redness and skin barrier damage have been averaged and normalized to the score of a commercially available, mild synthetic detergent bar. Product A is the mildest and Product F is the harshest. The products were ranked identically for the three parameters.