Which layer of hair acts as a barrier that protects the inner structure of the hair?

The hair cuticle serves as the outermost protective layer of the hair strand, acting as a barrier that safeguards the inner structures, such as the cortex and medulla. The cuticle is composed of overlapping scale-like cells that are tightly packed together, making it resilient against environmental damage, moisture loss, and physical wear. This structure is crucial in maintaining the overall health and integrity of the hair, as it prevents pollutants and toxins from penetrating deeper layers.

In contrast, the cortex, while vital for providing strength and color to the hair, lacks a protective capability against external factors. The medulla, found in some hair types, has an unclear function and is not consistently present in all hair, making it less relevant in terms of protection. The epicuticle, while related to the cuticle, primarily pertains to the outermost part of the hair shaft and is not a distinct structure like the cuticle itself. Thus, the cuticle is integral to maintaining the hair's durability and appearance.