What is the primary material that forms the nail unit?

The primary material that forms the nail unit is keratin. Keratin is a fibrous structural protein that is a key component of hair, skin, and nails. It provides strength and resilience, making it essential for the durability of the nail structure. The nails are composed predominantly of hard keratin, which is produced by the nail matrix and forms the hard plate that constitutes the visible part of the nail.

Collagen, while an important protein in connective tissues throughout the body, does not form the nails themselves. Instead, it provides structure and support to the skin and surrounding tissues. Fibrin is primarily involved in the blood clotting process and is not a component of the nail structure. Elastin is responsible for providing elasticity to the skin and other tissues but is not a structural material found in nails. Therefore, keratin is the correct choice, as it directly forms the nail unit and gives it its characteristic hardness and protective qualities.