Modulation of human stratum corneum properties by salicylic acid and all-trans-retinoic acid

Topical all-trans-retinoic acid (RA) has been reported to decrease the in v ivo skill response to sodium lauryl sulfate (SLS). The converse was also sh own with a synergistic effect of RA following prior applications of SLS. Th e reason for such effects is not clear. We employed measures of transepider mal water loss (TEWL), squamometry and sequential corneosurfametry to explo re the protective activity of a 0.05% RA cream at the level of the stratum corneum. Nonionic oil-in-water emulsions with or without 5% salicylic acid (SA) served as test product references. Data indicated that the RA formulat ion was responsible for a stochastic impairment in the TEWL and for an incr eased intercorneocyte cohesion, SA and the unmedicated emulsion did not lea d to similar TEWL changes. The squamometry test proved to be very sensitive to disclose the effects of SA and RA without, however, allowing to disting uish the difference in the physiological processes involved. The corneosurf ametry bioassay did not show any protection or synergistic effect between B A or SA and SLS challenge on the stratum corneum, This is in contrast to a previous work showing a positive protective effect afforded by retinol agai nst SLS, The combined effects of irritant compounds affecting the stratum c orneum are complex. The precise reason for some of their biological consequ ences remains a conundrum. On balance, products such as SA and RA do not ap pear to afford protection or impairment to a surfactant challenge at the le vel of the stratum corneum.