Which of the following is NOT a component of hair structure?

The correct answer identifies "skin" as not being a component of hair structure, distinguishing it from the other options that are integral parts of the hair itself.

To elaborate, hair is primarily composed of three layers: the cuticle, cortex, and medulla. The cuticle is the outermost layer, serving as a protective barrier against damage and moisture loss. The cortex, located beneath the cuticle, makes up the bulk of the hair and contains fibrous proteins that give the hair its strength and elasticity, as well as the pigment that contributes to its color. The medulla, which may or may not be present in all hair types, is the innermost layer and can influence the overall structure and texture of the hair.

In contrast, skin refers to the outer protective covering of the body, which includes various layers (such as the epidermis and dermis) that serve different functions unrelated to the composition of hair. Thus, while skin plays a role in protecting hair follicles and supporting hair growth, it is not a structural component of the hair itself. This distinction reinforces the understanding of hair anatomy in relation to its biological environment.