Human hair. Coloured Scanning Electron Micrograph (SEM) of strands of human hair. Hair is comprised of a fibrous protein (keratin), which develops out of a tubular hair follicle found in the epidermis of the skin. The shaft, the external part of the hair, consists of three layers. The outer layer or cuticle appears scaly. Beneath this is the cortex which contains 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. A hair grows about 0.2-0.3 millimetres per day. Magnification: x250 at 6x6cm size.