Collagen is a protein that serves as one of the main building blocks for bones, skin, hair, muscles, tendons, and ligaments. It is naturally produced in the body, but its production decreases with age, which can cause many health issues, including bone, joint, and skin problems. Collagen supplements are available in various forms, such as capsules, powders, and liquids, and are marketed as a way to improve skin elasticity, reduce visible wrinkles, and increase blood flow to the skin. However, it is unclear if collagen supplements benefit us, as most things we ingest are broken down by stomach acids and are not absorbed into the bloodstream. Collagen supplements contain amino acids, the building blocks of protein, and some may also contain additional nutrients related to healthy skin and hair like vitamin C, biotin, or zinc. Collagen type II (native) is a protein that is part of the cartilage, bone, and other types of connective tissues in animals and humans. It is used for osteoarthritis and other types of joint and muscle pain, but there is no good scientific evidence to support these other uses. Collagen is naturally found only in animal flesh like meat and fish that contain connective tissue, but a variety of both animal and plant foods contain materials for collagen production in our own bodies. Some collagen supplements are derived from bovine animals, pigs, and marine species like fish, jellyfish, and sponges. Collagen supplements are possibly safe when used short-term, but some people might have stomach problems after taking them.