Aging skin microbiology

Abstract

The skin, the largest organ of the body, helps maintain homeostasis by regulating heat and moisture transfer and is the body's first line of defense against environmental insults such as temperature extremes and pathogen invasion. Structurally, it is composed of multiple layers of epithelial cells (Fig. 83.1). The outer layer of the skin, the epidermis, arises from a generative basal layer of cells; the daughter cells terminally differentiate and keratinize as they rise to the skin surface. Thus, about 90% of the epidermis consists of dead keratinocytes embedded in a lipid-rich, hydrophobic mortar that creates a relatively impervious barrier with the environment. Other epidermal cell types include melanocytes (pigmented, UV-absorbing cells), sensory Merkel cells, and Langerhans cells of the immune system. Below this, the dermis contains structural proteins (such as collagen and elastin), hair follicles and sebaceous glands, other eccrine and apocrine glands, adipose tissue, and blood vessels. © Springer-Verlag Berlin Heidelberg 2010.