The most abundant protein in the human body is collagen. Collagen is a substance that becomes very strong when pulled apart, but is weaker when it is pressed together. It works to help support the human body. Collagen is the main component of connective tissue in the human body. Connective tissue is found in tendons, ligaments, as well as the skin. In fact, 70% of the skin is collagen. Collagen is also contained in cartilage, bone, and blood vessels. It can be found in the cornea as well as in the discs of vertebrae. Humans tend to produce less collagen or a weaker version of collagen as they age. This is why older individuals tend to have skin that sags, because there is not enough collagen to support it.