Applied Cosmetic Science and Technology Applied Cosmetic Science and Technology

The stratum corneum is crucial in enabling the barrier function of the skin. While the impact of the penetration of cosmetic ingredients on lipid organization is well documented, the actual effects of daily cleansing routines remain unclear. This study aimed to evaluate the effects of cleansing practices on the intercellular lipid structure in the stratum corneum. Several ex vivo skin explants and a multifunctional static and dynamic friction-measuring machine were used to experimentally replicate cleansing routines. The skin explants were subjected to a series of cleansing procedures, with or without 5% sodium dodecyl sulfate (SDS) or a 20% polyglycerol fatty acid ester formulation (base formula). Subsequently, hematoxylin and eosin staining of full-thickness skin and small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) of the stratum corneum were performed. Histological observations showed that, regardless of whether the cleansing procedures were applied, treatment with 5% SDS damaged epidermal cells, whereas the base formula did not affect them. The lamellar and packing structures were disordered by treatment with 5% SDS and the base formula in the group without the cleansing procedures. In the group with the cleansing procedures, the peaks were also disordered by the cleansing treatment, but the effect was relatively mild compared to that in the group without the cleansing procedures. This study demonstrated that lamellar periodicity and packing structure vary with application methods, highlighting the need to consider the cleansing process when assessing cleanser effects on the skin.