Collagen is a group of proteins that occur naturally and are found in animals. They are most abundant in the flesh and connective tissues of vertebrates. It is the main component of connective tissue and is the most abundant protein in mammals.
In humans, collagen makes up about 25% to 35% of your whole-body protein content.
Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments, and skin, and is also abundant in the cornea of your eyes, in cartilage, bone, blood vessels, the gut, and intervertebral discs.