The epidermis is the outermost of the three layers that make up the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water released from the body into the atmosphere through trans-epidermal water loss. The epidermis is composed of multiple layers of flattened cells that overlie a base layer (stratum basale) composed of columnar cells arranged perpendicularly.
The rows of cells develop from stem cells in the basal layer. Cellular mechanisms for regulating water and sodium levels (ENaCs) are found in all layers of the epidermis.
The word epidermis is derived through Latin from Ancient Greek epidermis, itself from Ancient Greek epi, meaning ‘over, upon’ and from Ancient Greek derma, meaning ‘skin’. Something related to or part of the epidermis is termed epidermal.
The human epidermis is a familiar example of epithelium, particularly a stratified squamous epithelium.