Abstract
Delivering a useful material into the skin is one of the most important roles of cosmetic preparations. The stratum corneum, the outermost layer of the epidermis, acts as the barrier to prevent skin from being penetrated by external hazardous substances and losing internal water to excess. Many penetration techniques through the stratum corneum have been investigated and developed in order to pass through the barrier and deliver useful materials contained in the cosmetic preparations applied on the skin surface. Most of them were aimed at improving permeability into the stratum corneum, and the diffusion and permeation properties within the underlying epidermal living cell layer have been not well investigated. We hypothesized that the penetrating ability into the epidermal living cell layer differed from the case of the stratum corneum, because of the difference in the water content between the two epidermal layers. In this study, an individual permeability test for each layer was performed. The results confirmed our hypothesis, which suggested that the permeation property both in the epidermal living cell layer and the stratum corneum influenced the permeability through the whole epidermis. Efficient delivery of useful materials to the target cells in the living cell layer would require consideration of the permeation strategy for both layers.
