What is the outermost layer of the hair shaft?

The outermost layer of the hair shaft is the cuticle. This layer is composed of thin, flat, overlapping cells that serve as a protective barrier for the inner layers of the hair. The cuticle's primary function is to protect the inner cortex and medulla from damage caused by environmental factors, chemical treatments, and mechanical stress. The condition of the cuticle can influence the overall health and appearance of the hair, as a healthy cuticle reflects light well, making hair look shiny and vibrant.

While the cortex is the next layer beneath the cuticle and is responsible for the strength and color of the hair, it is not the outermost layer. The medulla, which is the innermost core of the hair shaft, is present in some hair types, particularly coarse hair, but it is also not the outermost layer. The follicle, on the other hand, is not a layer of the hair shaft but rather the structure in the skin from which the hair grows. Therefore, the cuticle is accurately identified as the outermost layer, emphasizing its role in both protection and the overall appearance of the hair.