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Hair follicles. Coloured scanning electron micrograph (SEM). The outer layer of hair (the cuticle) has overlapping scales of keratin. These scales are thought to prevent hairs from matting together. Hair is made up of a fibrous protein called keratin. Internally the hair shaft is divided into three concentric sheaths (layers) called the medulla, cortex and outer cuticle. Hair is non-living tissue. Hair (purple) grows from a hair root (bulb, follicle) embedded in the skin. Hair growth occurs when epidermal cells divide at the base of the root bulb. Hair is non-living tissue. Magnification: x350 when printed at 10 centimetres wide (KEYSTONE/SCIENCE PHOTO LIBRARY/STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY)