j. Soc. Cosmet. Chem., 42, 147-158 (May/June 1991) Changes in skin pH and resident flora by washing with synthetic detergent preparations at pH 5.5 and 8.5 H. C. KORTING, K. GREINER, K. Hf3BNER, and G. HAMM, Dermatologische Klinik und Poliklinik der LM U, Frauenlobstrasse 9-11 (H.C.K., K.G., K.H.), and Poliklinikfiir Zahnerhaltung und Parodontologie der LMU, Goethestrasse 30 (G.H.), D-8000 Munich 2, Germany. Received April 2, 1989. Synopsis A crossover trial was performed in 10 healthy volunteers using a synthetic detergent preparation at pH 8.5 vs 5.5. Both on the forehead and on the forearm significantly higher skin surface pH values were detected in those volunteers using the alkaline preparation. While the counts of coagulase-negative staphylococci were never influenced in a significant manner by the type of cleansing agent, there were significantly more propionibacteria on the skin of the forehead at the end of the fourth week and on the forearm at the end of the first, second, third, fourth, and eighth week of the trial (p 0.05). Propionibacterial counts both at the forehead and at the forearm were significantly correlated to pH (p 0.05). These findings support the hypothesis that acidity or alkalinity can influence both the skin surface pH and propionibacteria as one as the major components of the skin flora in the long term. INTRODUCTION The effect of repeated washings with both soaps and synthetic detergent preparations on the cutaneous surface pH and bacterial flora has already been focused upon by several investigators. This especially applies to single washings with either soap (1,2) or soap and synthetic detergent preparations (3,4). In some of these investigations, all of which are solely concerned with skin pH, the effect of repeated applications of the cleansing agents was also examined (1,4). While the effect of soap (5) and synthetic detergent preparations (5,6) on the cutaneous microflora was by principle also investigated, although to a lesser extent, both cutaneous surface pH and bacterial flora together have so far only once been analyzed under the aspect of their relationship to washing proce- dures. In this recent study (7), both parameters were examined at the same time in volunteers regularly washing the skin of forehead and forearm twice a day for four weeks each, with (alkaline) soap or an acidic synthetic detergent preparation of pH 5.5 (cross- over design). The skin pH was found to be significantly higher when soap was used (by 0.3 units), as was the number of propionibacteria both at the forearm and the forehead. Counts of coagulase-negative staphylococci, however, showed no such significant dif- 147

148 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ference. The significant correlation of skin surface pH and propionibacterial counts, in fact, corresponded to in vitro findings concerning the specific growth rate of propioni- bacteria and staphylococci at various relevant pH values (8). These recent experimental findings are consistent with the so-called acid mantle concept created by Marchionini and his group as early as half a century ago (9) and later by Arnold (2) and RiSckl (10). Facing the conclusions from our previous experiments, one might, however, argue that not the pH value of the different cleansing agents but the differing chemical composi- tion might influence the resident flora of the skin. To test this hypothesis, a corre- sponding investigation was performed using two synthetic detergent preparations with identical ingredients at pH 5.5 and 8.5. MATERIALS AND METHODS EXPERIMENTAL STUDY POPULATION Five male and five female healthy volunteers gave written informed consent to enter the study. While the age ranged from 24 to 35 years, the mean age amounted to 27.5 years. Half of the individuals were attributed to a group called A, starting defined washing procedures with the synthetic detergent preparation A characterized by pH 5.5, the other half with preparation B characterized by pH 8.5. CLEANSING AGENTS Both liquid cleansing preparations contained identical amounts of the following ingre- dients (stated in descending quantitative order): water, mipa-laureth-sulfate, and coca- midopropylbetaine potassium coco-hydrolyzed animal protein PEG-7 glyceryl-cocoate cocamidopropylaurylether PEG-10 olive oil sodium lactate, perfume, benzyl alcohol, and methylisothiazolinone hydrogenated cocoglyceride and tocopherol niacine and pyridoxine hydrochloride, biotin and amino acids disodium EDTA, dye C.I.47005 and dye C.I.61570 and BHT and citric acid and ascorbyl palmitate. The only difference between the two preparations consisted of the pH (5.5 with prep- aration A 8.5 with preparation B), which was adjusted by the addition of appropriate amounts of sodium hydroxide. Both preparations were kindly supplied by Sebapharma, Boppard, FRG, preparation A corresponding to a previous commercial formula (Sebamed © fliissig). pH DETERMINATION The pH of the skin surface was determined using the flat glass electrode for sur- face measurements developed by Ingold that was first used in the field of dermatology by Schirren (11) and now is commercially available (Glaselektrode 403-S7, Ingold-Mef3technik, Steinbach, FRG). This electrode was connected to a precision pH-mV meter (pH 125, WTW, Weilheim, FRG). At any point of time three consec- utive measurements were performed and the mean value calculated. By principle the rules for skin surface pH determinations established by Arbenz (12) were followed.