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

The cortex is the layer of hair that plays a crucial role in determining its strength and elasticity. This middle layer forms the bulk of the hair structure and is made up of long chains of protein, primarily keratin. The arrangement and quantity of these protein chains determine how resilient the hair will be, allowing it to withstand stress without breaking. The cortex also contains melanin, which affects the hair's color and contributes to its overall health and appearance.

In contrast, the cuticle is the outermost layer and serves primarily as a protective barrier, while the medulla, which is the innermost layer, is not present in all hair types and is more associated with the structural properties. The bulb is the part of the hair root that is involved in hair growth and does not directly contribute to the strength and elasticity of the strand itself.