A nail is composed PRIMARILY of what substance?

Nails are primarily composed of keratin, which is a type of fibrous protein essential for the structure of nails, hair, and the outer layer of skin. Keratin provides durability and resilience, which allows nails to withstand everyday wear and tear.

When it comes to other substances listed, while they may have a role in the overall composition or health of the nail, keratin is the main structural component. Collagen is primarily found in connective tissues and serves different functions in the body, such as providing structure and support to skin and joints. General protein is a broad category that encompasses many types of proteins; while keratin is a protein, not all proteins are specifically involved in nail composition. Calcium is important for nail health but is not a primary component of the nail structure itself. Thus, keratin stands out as the key substance that makes up a nail.