Which part of the hair shaft is responsible for its strength and elasticity?

The cortex is the part of the hair shaft that plays a crucial role in providing strength and elasticity. Comprising tightly packed keratin fibers, the cortex contains the bulk of the hair's structure and is responsible for the hair's overall durability. Within the cortex, the configuration and quality of these keratin proteins enable the hair to stretch and return to its original shape, which is essential for maintaining healthy, resilient hair.

In contrast, the cuticle, which is the outer layer of the hair, serves primarily as a protective barrier. While it can affect the overall appearance of the hair, it does not contribute significantly to its strength or elasticity. The medulla, often considered the innermost layer, has a less defined role and is not present in all hair types. Furthermore, the sebaceous gland is not a part of the hair shaft itself; instead, it produces sebum to lubricate the hair and skin, which influences hair health but does not impact the structural properties of the hair shaft.