In humans, the skin is the one of the largest organs of the body and is composed of two primary layers, the dermis and the epidermis. The epidermis is the outermost section, composed of tightly packed cells, and is substantially thicker in areas that are exposed to constant friction, such as the soles of the feet.

Separated into several smaller strata, the epidermis is composed of various cell types, but principally consists of keratinocytes. Blood is not provided to the epidermis and the most superficial cells are dead, sloughing off continually in small fragments. Some other animals, such as snakes, however, shed their dead skin all at once in a process known as ecdysis.

The epidermis of both plants and animals play a similar role in the functioning of individual organisms. The primary purpose of the epidermis is protection from injury and foreign substances. In vitro epidermis, or synthetic skin, was originally developed to provide the same service to serious burn victims, but has since found additional uses. Synthetic skin is capable of being used for testing sunscreens and other skincare products, which helps eliminate the need for animal studies.