What is the main function of the cuticle layer of the hair?

The cuticle layer of the hair serves a critical role in protecting the inner layers, specifically the cortex and medulla. Comprised of overlapping, flat cells that resemble roof shingles, the cuticle forms a barrier that shields the more delicate structures beneath from environmental damage, such as UV radiation, chemical exposure, and physical abrasion. By safeguarding these inner layers, the cuticle helps maintain the hair's overall integrity, strength, and health.

While the other functions listed, such as nutrient delivery or moisture control, may be influenced by the condition of the cuticle, they are not its primary role. Nutrients are supplied mainly through the hair follicle from the scalp, not the cuticle itself. Moisture control is more associated with the hair's hydrophilic properties, and color is determined by the pigments in the cortex rather than the cuticle layer. Thus, the protective function of the cuticle is essential for maintaining healthy hair and preventing damage to the inner structures.