What type of fibers makes up 70% of the dermis and contributes to its structural toughness?

Collagen is the primary structural protein found in the dermis, making up approximately 70% of its composition. This fibrous protein provides strength and support, contributing to the structural integrity and toughness of the skin. The collagen fibers form a dense network that helps the skin resist tearing and stretching, which is crucial for maintaining the skin's barrier function and overall health.

Elastin, while also present in the dermis, primarily allows for elasticity and resilience rather than structural toughness. Keratin is a key protein in the epidermis and is responsible for the waterproofing and protective properties of the skin; however, it does not significantly contribute to the dermis's structure. Reticulin fibers, although present in skin, are more associated with providing a supportive network for organs and tissues rather than being the main contributor to the dermis's toughness.

Therefore, the selection of collagen as the answer reflects its critical role in providing the necessary strength and durability to the dermis, essential for the skin's overall functionality.