Penetration of lucifer yellow into human skin: a lateral diffusion channel in the stratum corneum.

We investigated the penetration of Lucifer Yellow into human and murine epidermis in 4-mm punch biopsies by incubation in dye solution. Lucifer Yellow was taken up freely by the dermis but penetrated only slightly into keratinocytes of the basal and suprabasal layers. However, progressive lateral diffusion was observed in the lowest layers of the stratum corneum, extending a distance of 1 mm in 6 hr. Under high magnification, Lucifer Yellow appeared to lie within rather than between corneocytes of this layer. Control samples stained with Lucifer Yellow after sectioning showed no preferential binding of the dye in this region. We concluded that the localization of staining was the result of diffusion from the cut edge of the stratum corneum. Lucifer Yellow penetration was insensitive to PMSF, 1:10 phenanthroline, or N-ethyl maleimide and was also observed in an in vivo injury, indicating that it was not an artifact of proteolytic or degenerative changes. In contrast, horseradish peroxidase failed to penetrate, suggesting molecular size limitation to channel entry. Diffusion of Lucifer Yellow beneath the stratum corneum marks a pathway for the lateral movement of small molecules of potential importance in the normal physiology of the skin, drug delivery, and pathology.