Epidermal Permeability Barrier and Other Topics

A historical review on the epidermal permeability barrier: Elias has published a historical review on the epidermal permeability barrier dating from the early days at Harvard to newly emerging concepts.1 This is a must-read article if you are the least bit interested in skin physiology. I will attempt to cover the highlights here. Elias begins with the statement, “Perhaps no tissue is so physically maligned by processing for light/electron microscopy as is the stratum corneum (SC). To further complicate matters, no tissue of such critical importance for survival has been so intellectually maligned as well.” He then traces the work of now famous investigators including Kligman, Blank  and Scheuplein.

Developments after 1970 showed that the “plastic wrap” model of Blank did justice neither to the structural homogeneity nor the metabolic activity of the SC. Work by Menton and Eisen showed that frozen sections of SC revealed the compression of corneocytes into exquisite geometric stacks of interlocking tetracaidodecahedra (24 sided) cells.  Elias and Friend then showed the presence of lipid stacks, localized in the intercellular spaces of the SC, which were shown to be derived from the secreted contents of the epidermal lamellar or Odland bodies.

Following this, the exquisite work by Gray and Yardley, Elias et al, and Wertz and Downing revealed a unique extracellular membrane system, devoid of phospholipids, relying instead on an equimolar mixture of ceramides, cholesterol and nonessential free fatty acids to form extracellular membranes. These membranes are riveted into parallel structures by linoleic acid-bearing α-hydroxy-esterified ceramides.

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