The outermost layer of the skin. The epidermis contains no nerves or blood vessels, so the epidermis alone is incapable of sensation or bleeding. Composed of a protective outer layer of nonliving keratin-derived scale cells, the epidermis acts as an envelope or seal against the environment and exerts some control on the amount of moisture lost to the environment. The epidermis contains keratinocytes (cells that make keratin) and melanocytes (cells that make pigment), as well as other specialized cells.