Which layer of hair is responsible for its protective qualities?

The cuticle is the outermost layer of the hair shaft and plays a critical role in protecting the inner layers of the hair. It is composed of overlapping, scale-like cells that lie flat and create a barrier against environmental damage, moisture loss, and chemical processes. This protective layer helps maintain the integrity of the hair structure by shielding it from physical and chemical harm, such as UV rays, pollution, and styling products.

The medulla, which is the innermost layer of the hair, primarily serves no significant protective function and is often absent in finer hair types. The cortex, situated beneath the cuticle, contains the bulk of the hair's mass and is responsible for the hair's strength, color, and texture rather than its protective qualities. The term "fiber" refers generally to the structure of the hair itself but does not specify a particular layer with protective properties. Thus, the cuticle is essential in providing the protective qualities that safeguard the underlying layers of hair.