Skin layers. Coloured scanning electron micrograph (SEM) of sectioned human skin. The top layer is the stratum corneum (flaky, pale brown), a cornified layer of the epidermis that is composed of flattened, dead skin cells that form the surface of the skin. The dead cells from this layer are continuously being shed and replaced by cells from the living epidermal layer below (red). The lowest layer (not seen here) is the dermis, a thick layer of fibrous connective tissue that supports and nourishes the epidermis. The skin is the body's largest organ, accounting for around 15% of the body's weight. Magnification: x1200 when printed 10cm wide.