A new model for assessing the damaging effects of soaps and surfactants on human stratum corneum.

To elucidate the damage to the horny layers of human skin produced by surfactants and soaps, we evaluated the cytological alterations of corneocytes using an in vitro assay. Suction blisters, 8 mm in diameter, were raised on the forearms of young adult Caucasoids. The roofs were cut off and the viable epidermis was removed. The discs of stratum corneum were then agitated for up to 6 h at 60 degrees C in 1% solution of five soap bars of differing irritancy. Additionally, individual examples of anionic, cationic and nonionic surfactants were similarly evaluated. Measurements of corneocytes included: (1) the number released with time (disaggregation), (2) size (swelling) and (3) morphologic degradation. The effects of the cationic and non-ionic surfactants did not differ significantly from those of distilled water. The anionic surfactant caused more release and less swelling and morphological change. The test soaps had vastly different effects on the structural integrity of the stratum corneum. The harsher ones caused greater disaggregation, more swelling and greater morphologic deterioration of corneocytes, whereas the milder ones had less marked effects on these parameters. This model would be a useful screening technique for formulating milder soaps and might also provide insights into the complex modes of action of surfactants on the stratum corneum.