Anionic surfactants are often used for cleaning and pharmaceutical purposes because of their strong surfactancy and foaming property. However, they are rarely ingested orally, the skin is a part of the human body most affected by surfactants. Barrier function of the skin is very strong, but the anionic surfactants can cause serious damages to it. Recently, amino acid-based surfactants have attracted attention as a safer option owing to their biocompatibility. Cytotoxicity examinations revealed that the amino acid-based surfactants are superior to sulfate-based surfactants. However, a systematical and comprehensive study related to the effect of these surfactants on skin barrier function has not yet been reported. In this work, skin permeation test using the skin of hairless mice and HPLC method is carried out. The material transmission speed through skin in a steady state was different between each surfactant treatment. We performed a comprehensive analysis of the effect of surfactants on skin barrier function and defined Transmission Index as an index for the degree of effect of surfactants. Glutamate series amino acid-based surfactant were effective to Transmission Index and we guessed the cause was due to adsorption. Based on the finding this study, we suggest using adsorptive property as a measure to the effect on the skin barrier function.

Background/purpose Detailed information on the mechanism by which surfactants affect the skin barrier function is still scarce. We investigated the contribution of protein denaturation to the effect of surfactants on barrier function. Methods The Transmission Index method, which evaluates the actual effect of surfactants on barrier function, was combined with a microplate assay measuring protein denaturation activity. The correlation between the TI value and the reciprocal of the median effect concentration (1/EC50) was analyzed for 19 surfactants. The contribution of protein denaturation to the effect of surfactants was discussed based on the 1/EC50 per TI value. Results A few surfactants showed high TI value. Nonionic surfactants had no effect. The EC50 varied without certain trend. For amino acid‐based surfactants, there was a gradual inverse correlation between the TI value and the 1/EC50. Conclusion The difference in the alkyl structure and the ion source affected the skin barrier function. Protein denaturing activity of the surfactant was not a critical factor. This suggests that the effect on intercellular lipids was the major factor. However, the magnitude of the contribution of protein denaturation activity varied depending on the surfactant, suggesting that each surfactant has a different mechanism of influence on skin barrier function.

Anionic surfactants are commonly used as detergents and emulsifiers. However, these compounds are potent skin irritants. In this study, we evaluated the effect of the alkyl structure of anionic surfactants on the skin barrier function using the transmission index (TI) method. The TI method is used to measure the skin penetration rate of drugs. Sodium soaps of C18 fatty acids with different structures were evaluated. Sodium laurate was used as the control. In addition, microscopic observations of the skin tissue treated with different soaps and controls were performed to study the mechanism of skin permeation. Results showed that unsaturated fatty acid soaps exerted the most potent effect on the skin barrier function and saturated fatty acid soaps exerted the least effect; saturated branched fatty acid soap had an intermediate effect. This could be attributed to the differences in the melting points of different fatty acids. In addition, unlike lauric acid soap, C18 fatty acid soap did not cause morphological changes in the skin tissue. Thus, differences in the alkyl structure of fatty acids resulted in differences in the effect of fatty acid soaps on the skin barrier function. The mechanism was presumed to be an effect on intercellular lipids.