Cuticle – The shingled, protective outer layer fo the hair shaft that is responsible for our hair’s cosmetic appearance. The primary role of the cuticle is to protect the cortex for deterioration. The condition of the cuticle determines our hair’s ability to take in moisture and affects its ability to reflect light. The thickness of the cuticle layers varies with the coarseness of the hair fiber. Coarser hair fibers have more cuticle layers than fine hair fibers.