What does the term "cuticle" refer to in hair?

The term "cuticle" refers to the outermost layer of the hair shaft, serving as a protective barrier for the inner layers of the hair. The cuticle is made up of overlapping, scale-like cells that help to protect the more delicate inner layers, such as the cortex and medulla, from damage and environmental factors. This outer layer plays a crucial role in determining the shine and smoothness of hair, influencing how light reflects off the hair's surface, and consequently affecting its overall appearance.

Understanding the structure of hair is essential for various cosmetology practices, such as hair coloring, cutting, and styling. The health and condition of the cuticle can significantly impact how hair responds to treatments, making it vital for beauty professionals to possess knowledge of this layer. The other choices represent different components of hair structure: the innermost layer (medulla) and the middle layer (cortex) are crucial for overall hair strength and color but are not what is described by the term "cuticle."