What is the primary composition of the natural nail?

The primary composition of the natural nail is keratin, which is a type of fibrous protein that is essential for the structure and strength of the nail. Keratin is also found in other parts of the body, such as hair and skin, and serves to protect these areas. Nails are made of hard keratin that provides durability and resilience, allowing them to withstand various physical stresses. The presence of keratin gives nails their characteristic hardness and helps prevent them from breaking or splitting.

In contrast, collagen is a protein that is predominantly found in connective tissues, providing support and structure to the skin, tendons, and ligaments, but it is not a significant component of the nails. While the term "protein" is broad and may technically include keratin, it does not specify the specific type that is crucial to nail structure. Lipids, on the other hand, are primarily related to fats and oils and play a different role in skin and hair health rather than in the nail composition. Thus, keratin stands out as the key structural element of the nail, making it the correct answer.