Collagen is the most abundant protein in the body — the structural scaffolding of skin, bone, cartilage, tendons and blood vessels. It gives skin its firmness and helps tissues hold their shape.
The body makes less collagen with age, and women lose a notable share in the years after menopause as estrogen declines. Eaten collagen is digested into amino acids like any protein, so supplements don't go straight to your skin — and the evidence for collagen supplements is modest and mixed. See does collagen really work.