Hair. Coloured scanning electron micrograph (SEM) of hairs (yellow) emerging from skin. The surrounding layer of skin (pink) has a typically scale-like surface. Hairs grow from follicles in the underlying layer of the skin (the dermis). The portion of the hair emerging from the skin is made up of dead tissue. The outside of the hair, the cuticle (yellow), is covered in modified overlapping scales and protects the central cortex. The central cortex is made up of the fibrous protein keratin (not seen), which acts as a structural element. Hair grows at a maximum rate of 15 centimetres a year.