The hair cuticle is the outermost part of the hair shaft. It is a hard shingle-like layer of overlapping cells, some five to twelve deep. It is formed from dead cells which form scales that gives the hair shaft strength and do the best job of providing protection for it. The hair cuticle is the first line of defense against all forms of damage; it acts as a protective barrier for the softer inner structure including the medulla and cortex. The cuticle is responsible for much of the mechanical strength of the hair fiber. A healthy cuticle is more than just a protective layer, as the cuticle also represents the structure that controls the water content of the fiber. Much of the shine that makes healthy hair so attractive is due to the cuticle. The hair cuticle is also said to be water resistant.
Cuticles are often damaged by excessive mechanical manipulation such as brushing, using heat (like using curling irons) or chemical processing (like perms or texturizers). Everyday elements, such as the sun or wind can also cause wear and tear on hair and damage the hair cuticles as well. Although the cuticle is the outermost layer of the hair, it does not give the hair its color because it has no melanin, which is the pigment responsible; the color of a person's hair depends on what type of melanin they have, which is found in the cortex. Also cuticle cells may be elongate, acuminate (gradually tapering to a point), ovate (egg shaped), or flattened.