Skin surface. Coloured scanning electron micrograph (SEM) of the surface of the skin (red) of a 43-year-old. The outermost surface is composed of dead and dying skin cells from the underlying epidermis, which help to protect the delicate epidermal cells from the external environment. A globule of sebum (a natural oily substance, yellow) can be seen at the base of a hair (brown) growing out of a follicle (centre). Magnification x84 when printed 10 centimetres wide.