Which layer of hair is considered the most important?

The cortex is the most important layer of hair because it plays a critical role in determining the hair's strength, color, and texture. This is the middle layer of the hair shaft, composed of long chains of proteins (keratin) and melanin, which is responsible for hair pigmentation. The cortex provides the hair with its structural integrity and resilience, making it essential for the overall health and appearance of the hair.

In contrast, the cuticle is the outermost layer, acting mainly as a protective barrier but does not significantly contribute to the hair's structural characteristics or color. The medulla, which lies at the center of the hair shaft, is often absent in fine hair and when present does not play a substantial role in the overall quality of the hair. The dermal layer pertains to the skin beneath the hair and is involved in supporting and nourishing hair follicles rather than directly influencing the properties of the hair itself. Thus, the cortex stands out as the most crucial layer in terms of the hair's physical properties and appearance.