Collagen comes from the Greek and means binding together. Collagen fibers provide structure, firmness, mutual cohesion and elasticity. Collagen fibers are part of various types of supporting tissues such as skin, cartilage and bones. The most common form in the human body is collagen type I. This occurs in the skin, tendons, ligaments and bone tissue, among other things. Cartilage consists mainly of collagen type II. After the age of 25, the production of collagen connective tissue in the body can change.