156 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ? 6.5 4.$ 4 # ß . . I . ß I I I ß ß ß ß I ß I i I I .... I 4.5 5 5.5 6 6.5 [pH] Figure 9. Correlation of the counts of propionibacteria per square centimeter and pH values on the forehead from washing with synthetic detergent preparations at pH 5.5 and 8.5. pH range of 5.5 to 6.0 (in vitro). And this, in fact, is a range within which skin surface pH values can be changed by skin cleansing habits. By principle, one could speculate that the observed changes in skin surface pH are not the cause but the consequence of changes in the propionibacterial flora. This, however, is not likely, because the number of propionibacteria found per cm 2 is much different on the forehead and on the forearm, while the change in pH is nearly the same. Higher propionibacterial counts on the forehead are a well known phenomenon that reflects the totally different character of the entire biotope: the forehead and forearm were chosen as test sites because they represent a fatty and a dry biotope. As the forehead is a site predisposed to acne vulgaris, this finding raises the question of potential implications for the treatment or prevention of this disease in young adults. If it is true that propionibacteria play a role in the development of acne lesions, and if in particular adolescent acne is linked to comparatively high propionibacterial counts (21), it is tempting to speculate that acne-prone patients may profit from the regular use of a slightly acidic synthetic detergent preparation. Whatever the basic mechanisms might be, the present trial shows clearly that propionibacterial counts on the human skin surface can differ by more than one order of magnitude according to the cleansing preparation used. Hence, it seems advisable to conduct a controlled clinical trial in young adults susceptible to the formation of acne lesions.

pH EFFECTS ON SKIN 157 5,5 4.5 3.5 2.5 2 1.5 1 .5 Y ' -.421 +.59B X r-.St! (slg., 95•. : .348 r ,645 N- Figure 10. Correlation of the counts of propionibacteria per square centimeter and pH values on the forearm from washing with synthetic detergent preparations at pH 5.5 and 8.5. ACKNOWLEDGMENT We are grateful to Dr. Schadenb6ck from Sebapharma, Boppard, FRG, for providing both synthetic detergent preparations. REFERENCES (1) L. Peukert, EinfluB der Titrationsalkalitiit yon Reinigungsmitteln auf den pH-Wert der menschlichen Haut, Arch. Domatol. Syph., 181, 417•424 (1941). (2) L. Arnold, Relationship between certain physicochemical changes in the cornified layer and the endogeneous bacterial flora of the skin, J. Invest Dermatol., 5, 207-223 (1942). (3) W. Burckhardt, Methoden zur Untersuchung der Wirkung synthetischer Waschmittel auf die Haut, Dermatologica, 129, 37-46 (1964). (4) H. P6sl and C. G. Schirren, Beeinflussung des pH-Wertes der Hautoberfiiiche durch Seifen, Waschmittel und synthetische Detergentien, Hautarzt, 17, 37•40 (1966). (5) R. J. Holt, Aerobic bacterial counts on human skin after bathing, J. Md. /Vlicrobiol., 4, 319-327 (1971). (6) A. A. Hartmann and H. R6ckl, Vergleichende Untersuchung fiber den EinfluB yon Balneum Herreal Gel zum Duschen auf die aerobe Residentflora der Haut bei einmaliger Anwendung, •rztl. Kosmetol., 9, 16-25 (1979). (7) H. C. Korting, M. Kober, M. Mueller, and O. Braun-Falco, Influence of repeated washings with soap