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

The cortex is the part of the hair structure responsible for strength and elasticity. It lies beneath the cuticle and constitutes the majority of the hair shaft. The cortex is made up of long, coiled proteins called keratin, which give the hair its durability and flexibility. This structure also contains melanin, the pigment that gives hair its color, and helps determine how well hair can hold shape and style, contributing to its responsiveness to chemical treatments such as coloring and perming.

Understanding the role of the cortex is crucial for cosmetologists when selecting products and techniques for hair care and styling. The other parts of the hair structure serve different purposes. The cuticle acts as a protective outer layer, the medulla is often absent in finer hair and has no known critical function, and the follicle is the living structure from which hair grows, but it does not contribute directly to the hair's mechanical properties like strength and elasticity.