316 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I Figure 1. Change of pH values of the skin surface after washing 5 minutes with classical soaps. S20 • 2@0 24• • 2• • 16• o • 12• o o B• D A J . . . . --,--,-_ _.____. ß .~ ,T "- D B .............. - '-.... ½ • - .... _-- CONTROL 4• Figure 2. Relative densities of anionic skin surface charge determined by adsorption of Rhodamine B on forearm skin after use of different soaps.

CLEANSING BAR EVALUATION 317 Table III Irritancy Potentials of Free Fatty Acids (FFA) From Soaps B, C and D, and powdered A* Products D A B C 8% Solution Scores (FFA) (powdered) (FFA) (FFA) of A 24h 0 1 X 0.5 0 0 5 X 0.5 2 X 0.25 lO X 0.25 E o 1 o o 5 • 0 0.04 0 0 0.2 1x0.5 48h 0 1 x 0.25 0 0 13 x 0.25 • 0 0.25 0 0 3.75 • 0 0.01 0 0 0.15 * Free fatty acids and powdered A were tested as 8% suspensions in petrolatum applied to the backs of 26 subjects for 24 hours. Readings were taken using the scale in Table I 24 and 48 hours after removal of test materials. regular use of soap is only changed significantly 2-3 layers down, i.e., it is limited to the top layers (Figure 5). Induction of thermal sweating by running for a few hundred meters 24 hours after treatment with soap solution in Finn chambers caused complete neutralization of the residual soap at the skin surface a pH value of about 6.5 was obtained. 1.2 1. o I o oe o O.B rY -0. 2 Y = 0.266 + 0.•575 ß X r•O. 996 N-21 14-14 N-2g N-2g N-41• . Figure 3. Skin fluorescence (F (treated) - F (untreated)) versus intensity of erythema. Readings taken on skin treated with soap solutions. (Ex: 290nm / Em: 350nm). no v•.mtble ,m,m •k