**1. Introduction**

196 Atopic Dermatitis – Disease Etiology and Clinical Management

Yoshizawa, Y.; Nomaguchi, H.;Izaki, S. (2002). Clin Exp Dermatol. Serum cytokine levels in

Zhang, H.; Guo, Y.; Wang, W. (2011). Allergy. Mutations in the filaggrin gene in Han Chinese patients with atopic dermatitis, Vol.66, No.3, pp. 420-427, ISSN 1398-9995 Zlotnik, A. & Yoshie, O. (2000). Immunity. Chemokines: a new classification system and

atopic dermatitis, Vol.27, No.3, pp. 225-229, ISSN 0307-6938

their role in immunity, Vol.12, No.2, pp. 121-127, ISSN 1074-7613

ISSN 0394-6320

with disease activity in children with atopic dermatitis, Vol.24, No.1, pp. 15-23,

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.
