What part of the hair serves as the tough, outer protective covering?

The cuticle is the part of the hair that serves as the tough, outer protective covering. This layer is composed of flat, scale-like cells that overlap like shingles on a roof, which helps to protect the inner structures of the hair shaft from damage, moisture loss, and environmental factors. The integrity of the cuticle is crucial for maintaining hair health, as it influences the shine and overall appearance of the hair. A well-protected cuticle can enhance the durability and resilience of the hair, while damage to this outer layer can lead to issues like frizz, breakage, and dullness.

In contrast, the cortex, which lies beneath the cuticle, is responsible for the hair's strength, color, and texture. It contains keratin fibers and melanin, which contribute to these properties. The medulla, found at the center of thicker hair strands, is often absent in finer hair types and has no significant role in the overall strength or health of the hair. The follicle, on the other hand, is the structure within the skin where the hair grows but does not make up the hair shaft itself. Therefore, the cuticle is specifically recognized for its protective function as the outer layer of the hair.