Structure of fully hydrated human stratum corneum: a freeze-fracture electron microscopy study.

The structure of fully hydrated human stratum corneum was investigated by means of freeze-fracture electron microscopy. Mammary and abdominal stratum corneum were incubated for 48 h with phosphate-buffered saline, pH 7.4, occlusively or phosphate buffer, pH 7.4, occlusively and non-occlusively. The micrographs showed the corneocytes aligned parallel to the surface of the stratum corneum embedded in intercellular lipids. The corneocytes were swollen by the uptake of water. New features located in the intercellular lamellar regions were rough structures, water pools, and occasionally vesicle-like structures. The nature of the vesicle-like structures was not completely clear. The presence of water pools, mostly in close contact with the rough structures, suggests that a lipid-water phase separation occurred. The localization of water in the intercellular region and the corneocytes offers new insights into the penetration enhancement property of water (and into the pathways of drug penetration).