Collagen peptides provide the amino acids—glycine, proline, and hydroxyproline—your body uses to build collagen, a protein that supports skin, joints, and nails. There are over 20 known types of collagen, but types I, II, and III are the ones you’ll see most often in supplements—and they each serve different purposes. Type II: This type is found mainly in cartilage, making it especially helpful for direct joint support, cushioning, and mobility.