Collagen is a type of protein. Fibrous in nature, it connects and supports other bodily tissues, such as skin, bone, tendons, muscles, and cartilage. It also supports the internal organs and is even present in teeth. Collagen makes up about 25 percent of the total amount of proteins in the body. Some people refer to collagen as the glue that holds the body together. Without it, the body would, quite literally, fall apart. Often, collagen is discussed in relation to the skin. It works with keratin to provide the skin with strength, flexibility, and resilience. As people age, however, collagen degradation occurs, leading to wrinkles. As such, it is an important substance for those looking for ways to fight the visible effects of aging on the skin.