ABSTRACT
This chapter suggests that the skin differs from most body surfaces in contact with the external environment in being a dry epidermis rather than a moist mucosa. It shows that it has a wide variety of defense mechanisms among which the continual shedding of its outer layers is of particular importance. The chapter argues that the environment at a particular site on the skin surface is profoundly affected by the concentration of sweat and sebaceous glands at that site. The skin has a high content of proteins, lipids, and glycosaminoglycans and smaller quantities of DNA. The chapter also shows that microbial communities are not limited to the skin surface but are also present in hair follicles and within the underlying dermis. Variations in temperature of a few degrees between sites are unlikely to exert a dramatic selection pressure on the cutaneous microbiota because most microbes that colonize humans can grow over the range of temperatures that are encountered.
