Influence of repeated washings with soap and synthetic detergents on pH and resident flora of the skin of forehead and forearm. Results of a cross-over trial in health probationers.

Ten healthy individuals washed their forehead and forearm twice a day over consecutive periods of four weeks with soap and synthetic detergents or vice versa (cross-over design). In general the pH values were higher during the period when soap was applied (the mean pH differed by 0.3 units, p less than 0.01). As a rule the counts of coagulase-negative staphylococci were not much altered. The number of propionibacteria, however, was markedly higher when soap was used (p = 0.02 and 0.01 resp.). At the forehead there was a clear correlation between bacterial counts and skin pH both with propionibacteria (0.56, p less than 0.001) and staphylococci (0.51, p less than 0.001). At the forearm only the former proved true (0.24, p less than 0.05). Thus the skin pH seems to be open to long-standing changes according to the preferred washing habits which may also be of major influence on the composition of the cutaneous bacterial flora.