Which of the following best describes the cuticle layer of hair?

The cuticle layer of hair is indeed best described as the outer protective layer. This layer consists of overlapping, scale-like cells that serve to protect the inner layers of the hair shaft (the cortex and medulla). The cuticle acts as a shield against mechanical damage, chemical exposure, and environmental factors such as UV radiation and heat.

Its structure is critical in maintaining the overall health and integrity of the hair. When the cuticle lies flat and healthy, it contributes to the hair's shine and smoothness. Conversely, if the cuticle is damaged or raised, it can result in dullness, frizz, and increased susceptibility to breakage.

The other options refer to different layers or properties of hair that do not accurately describe the function of the cuticle. The inner bulk layer is the cortex, which provides the hair with strength and elasticity. The layer that contains pigment, such as melanin, is also part of the cortex. Lastly, the moisture-absorbing layer is related to the hair's ability to retain hydration, which is more associated with the cortex than the outermost cuticle. Understanding these distinctions is essential in hair care practices, as each layer plays a critical role in the hair's overall structure and health.