[noun] The epidermis, a term referring to the outer and superficial layer of the skin covering the dermis (the layer beneath the epidermis), and the hypodermis (the layer beneath the dermis) is primarily composed of stacked cells called keratinocytes. There are four superimposed layers (from the bottommost to the surface): stratum basale (basal layer), stratum spinosum (spiny layer), stratum granulosum (granular layer), and stratum corneum (horny layer). The epidermis is intersected by hairs, the sweat glands responsible for producing perspiration, and the sebaceous glands responsible for producing sebum. Its principal function is to protect the body from outside elements.