Chapter 8 Hydration Injury to Human Skin: A View from the Horny Layer

Abstract

During the mid-century, textbooks of dermatology described the horny layer as a graveyard of disintegrated keratinocytes, covering the surface with an amorphous mass of keratin fibrils, supposedly a product of the epidermis. This image was completely false, an artifact of H- and E-stained sections. I subsequently showed that the horny layer was a cellular tissue, a fabric of cornified cells creating a tough, flexible, coherent membrane. It was then learned that this stratum corneum was quite impermeable and constituted the rate-limiting barrier to the diffusion of substances into and out of the skin (Idson 1975). I proclaimed that it was the single biological mission of the epidermis to create the horny layer barrier, which I likened to saran wrap. The horny layer is an impermeable plastic film beautifully designed to “water proof” the viable tissue below, thus preventing it from drying out, and making terrestrial existence possible (Kligman 1964).