Which layer of the hair is primarily responsible for its strength and elasticity?

The cortex is the layer of hair that is primarily responsible for its strength and elasticity. Composed of tightly packed keratinized cells, the cortex provides the hair with its structure and makes it resilient to damage. The protein composition within the cortex contributes to its durability and flexibility, allowing hair to withstand various styling techniques and environmental factors without breaking easily. Moreover, the cortex contains melanin, which influences hair pigmentation, but its main role is related to the mechanical properties of hair.

The cuticle, a protective outer layer, helps shield the cortex from damage but does not have a significant role in strength or elasticity. The medulla, although present in some hair types, is often absent in finer hair and does not contribute to the overall strength and elasticity of hair. The papilla, located at the base of the hair follicle, plays a role in hair growth and nourishment but is not part of the hair shaft itself. Thus, the cortex is key to understanding the physical characteristics of hair, including its strength and elasticity.