ABSTRACT
A low humidity environment, such as in the winter season in Japan and reductions of moisture functions, including the barrier and water holding functions, lead to dry skin. In dry skin, the water distribution in the stratum corneum is altered compared with healthy skin. Especially, it is thought that the water content mostly decreases at the surface of the skin. When the uppermost layer of the stratum corneum is dehydrated by exposure to environmental dry conditions or by the reduction of moisture functions, the water needed is supplied from the deeper living cell layers of the epidermis to the stratum corneum to improve the dry state. For instance, skin exposed to a dry environment shows a reinforcement of its barrier function to improve skin dryness (Denda et al. 1998). Thus, the water žux in the skin could exert a signal that increases the secretion and/or synthesis of inžammatory cytokines from keratinocytes. Skin dryness is also caused by an excess usage of detergents such as sodium lauryl sulfate (SLS) (Okuda et al. 2002) and by the use of SLS-formulated creams (Tsang and Guy 2010).
