Coloured scanning electron micrograph (SEM) of a human hair bulb, root sheath and hair. Human hair is made up of a strong fibrous structural protein called keratin. In normal, healthy hair the outer layer (cuticle) has overlapping scales of keratin that run smoothly along the length of the hair. At the base of the hair, the hair root widens into a hair bulb. As hair ages, the bulb shrinks. The area just above the bulb is the root sheath which is the growing area of hair. Magnification: x66 when printed at 10cm wide.