150 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS most cases given in tables, by exception in figures. When differences are characterized as significant in the text, this reflects p 0.05. RESULTS pH VALUES On days 1-3 the pH values at forehead and forearm amounted to 4.45-5.68 and 4.42-5.86, respectively. In general, no major differences between each of the groups could be detected. For pertinent p values, here as in the following, compare Table I. In the group starting with the alkaline synthetic detergent preparation (B), the skin pH increased markedly while this product was used both at the forehead and at the forearm. After the change to the acidic preparation, the pH values decreased, again reaching, by and large, the original levels (Figures 1,2). In the groups starting with the acidic preparation (A), pH values remained, by and large, stable during the first half of the cleansing experiment during the second half pH values clearly went up (Figures 1,2). Significantly lower pH values at the forehead in those panelists using the acidic prep- aration were found on days 31, 45, and 59 at the forearm on days 17 and 31. BACTERIAL FLORA Significant differences in the counts of coagulase-negative staphylococci between the panelists using preparation A and those using preparation B were never found, either at the forehead or at the forearm, although the counts tended to increase while the alkaline preparation was used and to decrease while the acidic preparation was applied to the skin (Figures 3,4). With the propionibacteria, however, there was a sharp rise in CFU/ml Table I p-Values Characterizing Differences of pH Values and Staphylococcal and Propionibacterial Counts Between the Two Study Groups at the Various Days of Investigation pH Staphylococcal counts Propionibacterial counts Day Forehead Forearm Forehead Forearm Forehead Forearm 1 0.1829 0.3296 0.0128 0.1303 0.1062 0.1160 2 0.2771 0.5869 n.d. n.d. n.d. n.d. 3 0.4116 0.5013 0.0326 0.0607 0.1861 0.2076 10 0.0638 0.0226 0.5730 0.1810 0.1258 0.0031 17 0.0175 0.0076 0.6426 0.5464 0.1529 0.0002 24 0.0532 0.0428 0.3624 0.6649 0.0759 0.0024 31 0.0039 0.0119 0.8142 0.2733 0.0553 0.0080 38 0.1521 0.3395 0.2396 0.8237 0.7611 0.8216 45 0.0072 0.0541 0.0947 0.5921 0.2925 0.2392 52 0.0186 0.0467 0.0108 0.6818 0.1202 0.0246 59 0.0033 0.0240 0.0061 0.1770 0.0192 0.0002 Days 1-3: Previous washing habits used. Next 4 weeks: Panelists on either preparation A (pH 5.5) or B (pH 8.5). Last 4 weeks: Crossover period: Those previously on preparation A switched to B, and vice-versa.

pH EFFECTS ON SKIN 151 7.0 6.5 6.0 5.0 4.5 .. 0 • • • l! • , , , 1 2 3 10 17 2• :•1 3•8 •5 52 5•9 t (d) Figure l. Development of the pH values on the forehead from washing with synthetic detergent prepa- rations at pH 5.5 and 8.5. 7.0 6.5 6.0 4.5 , , !! , , , , , t (d) Figure 2. Development of the pH values on the forearm from washing with synthetic detergent prepara- tions at pH 5.5 and 8.5.