Knotted hair. Colour scanning electron micrograph (SEM) of a knotted strand of human hair. Hair is a fibrous protein (keratin), which develops out of a tubular hair follicle found in the epidermis of the skin. The shaft, the visible part, consists of three layers; an outer layer or cuticle, which appears scaly in normal hair. Beneath is the cortex containing hair colour pigments. The medulla forms the central core, which may be hollow. Hair cells are dead except for a layer at the base of the root, which divides to form new cells, pushing the older ones upward. Magnification: x60 at 35mm size.