Collagen is vital for skin elasticity and it is a unique protein and the building material to renew cells in all areas of the body including skin, nails, hair, eyes, teeth, cartilage, bones, tendons, organs, arteries, blood vessels, hemoglobin, immune cells and the immune system. Ligaments are another type of connective tissue that attach two bones and consequently hold the joints together. Tendons are similar but different type of tissue that attach the muscles to the bones.