What function does the cuticle serve in hair?

The cuticle serves a critical protective function for the inner layers of the hair shaft. It is the outermost layer of the hair and is composed of overlapping, scale-like cells that help guard against damage from environmental factors such as heat, chemicals, and pollutants. This protective barrier is essential for maintaining the overall health and integrity of the hair.

When the cuticle is healthy and lies flat, it helps to retain moisture within the hair shaft while keeping harmful substances out. Conversely, if the cuticle is damaged (for example, by excessive heat styling or chemical treatments), it can lead to frizz, breakage, and other issues, as the underlying layers become exposed and vulnerable.

The other choices pertain to different aspects of hair structure and function. For example, color in hair is primarily determined by the presence of melanin, which is produced in the hair follicle rather than the cuticle itself. Nourishment to the hair primarily comes from the hair follicle and the bloodstream, while the cuticle does not play a direct role in regulating hair growth. Therefore, the correct answer underlines the essential protective role of the cuticle in maintaining the health of the hair shaft.