Roso, A., Amalric, C., and N. Michel. The Relationship Between the Protein-Denaturating Power of Surfactants (Measured In Vitro) and Impairment of the Protective Barrier Function of the Stratum Corneum (Measured In Vivo). ATLA. 1999. 27: 354.

The objective of this study was to show the usefulness of the red blood cell (RBC) assay to investigate certain key factors associated with skin tolerance. With respect to denaturating power, different chemical classes of surfactant (anionic, amphoteric and non-ionic) all give different results. Alkyl sulphates proved to be powerful denaturing agents, anionic acylated proteins moderately potent, amphoteric derivatives very weak, and a non-ionic surface-active glycolipid was observed to have practically no denaturing activity at all. Combining an anionic surfactant with either an amphoteric, or a non-ionic surfactant, resulted in a product which caused significantly less denaturation than the anionic surfactant alone. One of the ex vivo consequences of the surfactant-medicated denaturation of protein is the swelling of the stratum corneum. This phenomenon is known to be marked when anionic surfactants are involved, relatively mild with amphoteric derivatives and practically non-existent for non-ionic species. The effects of combinations follow exactly the same pattern as that seen for denaturing power, and it should be noted that this hierarchy correlates closely with the results obtained when the same surfactants are applied on occlusive patches to the skin of volunteer subjects and the minute amount of water lost over a 24-hour period is measured: the greater the denaturing power of the surfactant, the larger the trans-epidermal water loss, i.e. the greater the compromise of the integrity of the protective barrier function of the stratum corneum.