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

The cortex is the layer of hair that is responsible for its strength and elasticity. This middle layer makes up the bulk of the hair and contains long chains of proteins, specifically keratin, which contribute to both the structural integrity and flexibility of the hair. The cortex is crucial because it influences the overall texture and appearance of the hair; it absorbs moisture and can withstand various styling processes.

In contrast, the cuticle serves as the outer protective layer of the hair and primarily helps to shield the inner layers from damage but does not play a significant role in strength and elasticity. The medulla, often referred to as the innermost layer of hair, may be present or absent in different hair types and does not contribute to the strength or elasticity of the hair. Therefore, the cortex is essential for providing the necessary attributes of strength and elasticity, making it the correct answer.