Here's why:

* Collagen and Elastin: These are the primary proteins that provide structure and flexibility to skin. Collagen gives skin its strength, while elastin allows it to stretch and return to its original shape.

* Keratin: This protein makes up the outer layer of skin (epidermis) and provides a protective barrier.

While sugars, starches, and nucleic acids play roles in the body, they are not the primary components of skin.