Epidermal Homeostasis in Space from the Stand Point of Keratinocyte Physiology

The human epidermis is the interface between the　human body and the environment. It is mainly comprised of keratinocytes. Since the beginning of this century, functional expression of a series of receptors for various environmental factors has been reported. Moreover, neurotransmitters and hormones originally found in the central nervous system are generated and released from keratinocytes. Thus, the pathophysiology of the epidermis is important not only for skin health but also for whole-body conditions. In outer space, humans must confront environmental factors different from those on Earth, such as electromagnetic fields, drastic changes in atmospheric pressure or humidity, and microgravity. In this review, the author discusses the potential effects of these factors on epidermal homeostasis and whole-body conditions.