The epidermis is composed of the outermost layers of cells in the skin, “epi” in Greek meaning “over” or “upon”, which together with the dermis forms the cutis. The epidermis is a stratified squamous epithelium, composed of proliferating basal and differentiated suprabasal keratinocytes which acts as the body’s major barrier against an inhospitable environment, by preventing pathogens from entering, making the skin a natural barrier to infection. It also regulates the amount of water released from the body into the atmosphere through transepidermal water loss (TEWL). In humans, it is thinnest on the eyelids at and thickest on the palms and soles at . It is ectodermal in origin.