ABSTRACT
In general, reduction of the skin surface water content causes ne wrinkling, known as epidermal wrinkling. Since the ne wrinkling can be restored by treatment with a moisturizer, the cause of wrinkles is understood to result from alterations of the epidermis, especially the stratum corneum, due to reductions of its water holding capacity. However, deep wrinkles are caused by dermal structural alterations in the papillary region induced by collagen degradation. This chapter developed the hypothesis that skin dryness accelerates wrinkling by enhancing collagen degradation. To obtain data to support that hypothesis, we developed an in vitro dry skin model and claried parameters caused by dry conditions. Parameters detected from the in vitro dry skin model were consistent with results obtained from the stratum corneum of dry skin in vivo. IL-1α, IL-8 and MMP-9 secreted from keratinocytes in the in vitro dry skin model play critical roles in collagen degradation and wrinkling. The cascade of events of our hypothesis is summarized in Fig. 9 and available experimental evidence supports that mechanism. We expect that this new concept will provide important clues to develop new formulations to prevent skin wrinkling.
