Collagen refers to a family of proteins that are the primary structural component of connective tissues, such as skin and cartilage, according to Yale University.
The substance makes up about a third of all the protein in the human body, more than any other type of protein in the body by mass. There are 28 different types of collagen, each type categorized based on its amino acid composition. About 90% of the collagen in the body is type 1, which is found in the skin, tendons, internal organs and organic parts of bone, according to Healthline. The vast majority of the remaining collagen in the body is made up of the following types:
Type 2: Found in the cartilage.
Type 3: Found in the bone marrow and lymphoid tissues.
Type 4: Found in the basement membrane (thin sheets of collagen that surround most types of tissues).
Type 5: Found in the hair and the surfaces of cells.