THE RELATIONSHIP BETWEEN SOLUTION PH AND CLINICAL IRRITANCY FOR CARBOXYLIC ACID-BASED PERSONAL WASHING PRODUCTS

The influence of formulation pH on the irritation potential of slurrie s formed from two commercial products composed entirely or partially o f aliphatic carboxylic acid-based surfactants (fatty acids and their s alts) was determined in vivo by use of a flex wash. Increasing the pH of a synthetic detergent/fatty acid slurry from its neutral value to a pH of 10 reduced its mildness. The neutral pH of the predominantly no n-soap-based cleanser, therefore, makes a significant contribution to its mildness. If it were formulated at pH 10, it would be significantl y harsher to the skin than the current neutral formulation. The pH als o had a significant effect on the irritation potential of soap-based c leansers. Decreasing the pH of soap slurries from their ''normal'' pH of approximately 10 to pH 7 reduced their irritation potential. The di fference in alkalinity, as measured by pH, is directly related to the lower irritation potential of both of these formulations. These result s demonstrate that pH has an important role in determining the differe nces in irritation potential of these complex skin cleansing compositi ons through effects on ionizable constituents.