Epidermis

The epidermis is the outermost of the three major layers that constitute the skin, the inner layers being the dermis and hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the amount of water released from the body into the atmosphere through transepidermal water loss. The epidermis is composed of multiple layers of flattened cells that overlie a base layer (stratum basale) composed of perpendicular columnar cells. The layers of cells develop from stem cells in the basal layer. The thickness of the epidermis varies from 31.2 μm for the penis to 596.6 μm for the sole of the foot with most being roughly 90 μm. Thickness does not vary between the sexes but becomes thinner with age. The human epidermis is an example of epithelium, particularly a stratified squamous epithelium. The word epidermis is derived through Latin from Ancient Greek epidermis, itself from Ancient Greek epi 'over, upon' and from Ancient Greek derma 'skin'. Something related to or part of the epidermis is termed epidermal.