Binding of surfactants to stratum corneum

The binding of surfactants to stratum corneum proteins has been implicated as one of the factors governing their harshness towards skin. In this paper, the binding characteristics of several anionic surfactants, including relatively harsh surfactants such as sodium dodecyl sulfate, TEA-sodium laurate, TEA-sodium oleate, and a relatively milder one such as sodium lauroyl isethionate (SLI), are presented. The effect of variables relevant to cleansing such as solution pH, temperature, and contact time on surfactant binding has been determined. The binding of laurate, oleate, and SDS is significantly higher than that of SLI. The extent of binding correlates with their expected irritation potential measured by the zein solubilization technique as well as with the published results of irritation to skin of cleansing bars based on these surfactants. The reasons for the increased binding of surfactants above their CMC are examined. It is also shown that SLI binding to skin is dependent on the solution pH, exhibiting a minimum in binding in the pH 7 to 9 region.