Physical and Chemical Factors that Improve Epidermal Permeability Barrier Homeostasis

For terrestrial creatures, the water-impermeable barrier function of the skin is essential to maintain life in the face of environmental dryness. Stratum corneum, which plays a crucial role in the barrier function, is composed of two components, i.e., protein-rich nonviable cells and intercellular lipid domains. When the barrier function is damaged by a surfactant, organic solvent or tape stripping, a series of homeostatic systems operates to restore the barrier function to its original level. At the first stage of the barrier repair process, exocytosis of lipid-containing granules, lamellar bodies, is accelerated and the internal lipid is secreted into the intercellular domain between the stratum granulosum and stratum corneum, forming a water-impermeable membrane. The barrier function is strongly associated with skin pathology. Abnormality of the barrier function is observed in a variety of skin diseases, such as atopic dermatitis. Although the barrier function of healthy skin can recover automatically after damage, the recovery is delayed by emotional stress or by aging. Moreover, under low environmental humidity, barrier damage induces epidermal hyperplasia and inflammation. On the other hand, acceleration of the barrier recovery prevents epidermal hyperplasia induced by barrier disruption in a dry environment. Thus, methods to improve the barrier function are very important for clinical dermatology. In the last two decades, various chemical and physical factors that accelerate the barrier recovery process have been reported. In this chapter, I will describe those findings and discuss some new biological aspects of epidermal barrier function.