Human hair. Coloured scanning electron micrograph (SEM) of a human hair emerging from the epidermis (outer layer of skin). Hair is a fibrous protein (keratin), which develops out of a tubular hair follicle found in the epidermis. The shaft, the part visible, is composed of two layers; an outer layer or cuticle, which consists of flat overlapping cells. This covers the main body of the hair, the cortex, which contains hair colour pigments. Hair is useful in keeping humans warm.