294 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1 Ii r = 0.71 p = 0.11 0 I I I I I I 0 1 2 3 4 5 6 7 In Vitro Ranking Figure 2. Correlation between the ranking of antibacterial liquid soaps using collagen swelling and the ranking of antibacterial liquid soaps using the modified soap chamber test. IN VITRO METHODS Collagen swelling test. The collagen swelling test was adapted from the method of Blake- Haskins et al. (1). In brief, a piece of collagen sheet (1 cm 2) from Colla-Tec (Plainsboro, NJ) is incubated for 24 hours, at 50øC, with a solution of the finished product at 1% of the dry extract at its own pH. The collagen is weighed before and after incubation to determine the amount of swelling. The more the collagen swells, the more irritating the product. The results are expressed as follows: CSW = (weight after incubation - initial weight)/initial weight pH rise test. In the pH rise test (2), equal volumes of a solution of bovine serum albumin (Sigma, St. Louis, MO) at 2% (w/v) and a pH of 5.6 and a solution of the finished product at 2% of the dry extract and a pH of 5.6 are incubated for one hour at room temperature. The resulting solution contains the finished product at a 1% concentra- tion. The pH of the solution is measured after incubation. The higher the pH rises, the more irritating the product. The results are expressed as follows: pH rise = pH after incubation - 5.6

EVALUATING IRRITATION POTENTIAL 295 1 ß 0 1 r=O.$1 p=O.07 0 1 2 3 4 5 6 7 In Vitro Ranking Figure 3. Correlation between the ranking of antibacterial liquid soaps using the pH rise test and the ranking of antibacterial liquid soaps using the modified soap chamber test. Zein test. Zein is a protein that is insoluble in aqueous solution unless denatured by irritating detergent products. In this test (3), fifty milligrams of zein from Sigma (St. Louis, MO) are incubated with a solution of the finished product at 1% of the dry extract. The solutions are mixed at room temperature at pH 7.0 for one hour. After incubation, the solubilized zein is isolated and assayed for protein using the BCA protein assay kit (Pierce Chemical). The more zein that is solubilized, the more irritating the product. The results are expressed as follows: Zein = milligrams of solubilized zein per milliliter of solution IN VIVO METHODS A modified soap chamber test was performed according to the method of Simion et al. (11) in early April by an independent testing laboratory. In this test, 0.3 ml of the products was applied at 5% dry extract to the panelist's forearms using occlusive Hill Top Chambers. Twenty-four hours later, the patches were removed, and the sites were