What is the function of a cuticle layer in hair?

The cuticle layer of the hair serves a crucial protective function. It is the outermost layer composed of overlapping cells that resemble roof shingles. This layer acts as a barrier, shielding the inner structures of the hair, specifically the cortex and medulla, from environmental damage such as UV radiation, pollution, and chemical treatments. By protecting these deeper layers, the cuticle helps maintain the overall integrity and health of the hair, preventing issues like breakage and moisture loss.

The cuticle does not add color to the hair, which is primarily determined by the pigment in the cortex. It also does not directly promote hair growth, as that process occurs at the hair follicle level. Additionally, the cuticle is not responsible for removing dead hair cells; rather, it protects the live hair shaft from damage and wear.