The relationship between solution pH and clinical irritancy for carboxylic acid-based personal washing products
Richard I. Murahata , Michael P. Aronson

Synopsis

The influence of formulation pH on the irritation potential of slurries formed from two commercial products composed entirely or partially of aliphatic carboxylic acid-based surfactants (fatty acids and their salts) 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 non-soap-based cleanser, therefore, makes a significant contribution to its mildness. If it were formulated at pH 10, it would be significantly harsher to the skin than the current neutral formulation. The pH also had a significant effect on the irritation potential of soap-based cleansers. Decreasing the pH of soap slurries from their “normal” pH of approximately 10 to pH 7 reduced their irritation potential. The difference in alkalinity, as measured by pH, is directly related to the lower irritation potential of both of these formulations. These results demonstrate that pH has an important role in determining the differences in irritation potential of these complex skin cleansing compositions through effects on ionizable constituents.

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