Hair is chiefly composed of which type of protein?

Hair is chiefly composed of keratin, which is a fibrous structural protein. Keratin is a key component that provides strength, durability, and protection to hair strands. It is also the primary protein found in other parts of the human body, such as nails and the outer layer of skin. The structure of keratin contributes to the varying characteristics of hair, such as its texture, resilience, and ability to withstand environmental stresses.

Collagen, on the other hand, primarily serves as a structural protein in connective tissues, such as skin, tendons, and ligaments. Elasticin is a protein that helps tissues resume their shape after stretching or contracting, providing elasticity, but it is not a significant component of hair. Fibroin is a protein found in silk and produced by some insects and spiders, which does not pertain to human hair composition. Thus, keratin remains the correct answer due to its central role in forming the hair structure.