What hair structure is primarily responsible for the strength of hair?

The cortex is the hair structure primarily responsible for the strength of hair. It is the thickest layer of the hair shaft and contains fibrous proteins and melanin, which contribute to the overall resilience and durability of the hair. The cortex provides the hair with its tensile strength, allowing it to withstand external forces and manipulation. This layer is also where the color and texture of the hair are determined, making it crucial for both aesthetic and functional aspects.

In contrast, the medulla is a soft, spongy core that is present in some hair types but does not significantly contribute to strength. The cuticle, while important for protecting the hair and providing a smooth surface, is primarily a protective layer and does not play a direct role in the structural strength of the hair. The follicle is responsible for producing hair and anchoring it into the scalp but is not part of the hair shaft itself, meaning it does not contribute to the strength of the hair strands.