What is the outermost layer of the hair shaft called?

The outermost layer of the hair shaft is known as the cuticle. This layer consists of overlapping, scale-like cells that serve to protect the inner layers of the hair, which include the cortex and medulla. The cuticle's structure plays a crucial role in the hair's overall health and appearance, as it represents the barrier between the hair's internal structure and external environmental factors. A well-maintained cuticle layer helps to retain moisture and gives the hair its shine, whereas damage to the cuticle can result in frizz, dullness, and increased susceptibility to breakage.

In contrast, the medulla is the innermost layer of the hair shaft, often absent in finer hair, and does not serve as the outer barrier. The cortex is the middle layer responsible for giving the hair its strength, color, and shape. The follicle, on the other hand, is part of the skin and not a layer of the hair shaft itself; it is the structure from which the hair grows. Thus, recognizing the cuticle as the outermost layer emphasizes its protective and aesthetic importance in hair health.