What is the main component of hair?

The primary component of hair is keratin, which is a fibrous protein that provides structure and strength. Keratin is crucial for the composition of hair, as it forms the hair shaft and contributes to the hair's resilience, durability, and overall health.

While other choices represent important proteins and substances in the body, they do not specifically define the main structural component of hair. For instance, collagen is primarily found in connective tissues and provides structural support to skin, tendons, and ligaments. Elastin, on the other hand, is a protein that allows tissues to resume their shape after stretching or contracting, predominantly present in skin and blood vessels. The term "proteins" is very broad and encompasses a wide variety of protein types, not indicating the specific element that is quintessential to hair structure.

Thus, keratin is recognized as the most significant protein in hair, making it the correct answer in understanding the primary biological component of hair.