What is the outermost layer of hair called?

The outermost layer of hair is referred to as the hair cuticle. This layer serves as a protective shield for the inner layers of the hair, specifically the cortex and medulla. The cuticle is composed of overlapping, scale-like cells that help to prevent damage from environmental factors and mechanical stress.

In addition to its protective function, the condition of the cuticle can significantly influence the hair's appearance, shine, and overall health. When the cuticle is intact and smooth, hair tends to look glossy and healthy; conversely, when the cuticle is damaged or raised, it can result in a dull and frizzy appearance.

The hair shaft, while also contributing to the hair's structure, refers to the visible part of the hair that extends beyond the scalp and does not specifically denote the outer layer. The hair bulb is located at the base of the hair follicle, where hair growth begins, and the hair follicle itself is the structure in the skin that surrounds the hair root, anchoring it into the scalp or skin. Each of these components plays a vital role in hair growth and health, but the cuticle is the direct answer to the question regarding the outermost layer of the hair.