Collagen /ˈkɒlədʒɨn/ is the main structural protein in the extracellular space in the various connective tissues in animals. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content.elatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed. Collagen also has many medical uses in treating complications of the bones and skin. The name collagen comes from the Greek κόλλα (kolla), kólla  meaning , glue and -suffix, -γέν, gen denoting. producing