pH EFFECTS ON SKIN 153 9.0 8.5' 8.0- 7.5- 7.0- 6.5- 6.0- 5.5- 5.0- 3.5- 3.0 • [ [ II [ ] [ ] [ [ [ ] 1 2 3 10 17 2LI 31 38 L$5 52 59 t (d] Figure 5. Development of the counts of propionibacteria per square centimeter on the forehead from washing with synthetic detergent preparations at pH 5.5 and 8.5. 5.5- 5.0- L$ 0- 3 5- 3o- 2 5- 2 0- 1 5- 1 0- 0.5- 0 T I I • /! I I I I [ , ' ' 1 2 3 10 17 2N 31 38 N5 52 59 t (d) Figure 6. Development of the counts of propionibacteria on the forearm from washing with synthetic detergent preparations at pH 5.5 and 8.5.

154 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS when the washings with preparation B began, and a sharp fall when the washings with preparation A began. Figures 5 and 6 demonstrate the findings in more detail. At the forehead, propionibacteria were significantly fewer in the presence of the acidic cleansing preparation on day 31 at the forearm the same applied to days 10, 17, 24, 31, and 59. INTERDEPENDENCE OF BACTERIAL DENSITY AND pH While the number of coagulase-negative staphylococci was only correlated with the skin pH values in a significant manner at the forehead and not at the forearm, propionibac- terial counts and skin surface pH correlated significantly at both sites, the correlation coefficient also being higher, especially at the forehead (Figures 7-10). DISCUSSION The pH values found at the skin surface of the forehead and the forearm in our study population lie well within the range given in the pertinent literature (for review, compare 19). As in our previous investigation, the mean pH value again tends to be lower than 5.5, which is considered as a representative value by most authors. Washing 8.5 8 7.5 ? 6.5 6 5.5 5 4.5 4 3.5 Y - .766 +.G?9 X r-.47B (slg., p-.BS) 95• : .3B8 r .618 N- 180 .... I . . I I I I I I I I .... I .... I .... 4.5 5 5.5 6 6.5 [pHI Figure 7. Correlation of the counts of coagulase-negative staphylococci and pH values on the forehead from washing with synthetic detergent preparations at pH 5.5 and 8.5.