Hyaluronic acid (HA) is found in highest concentrations in the fluids of the eyes and joints, and in the skin. HA is in the glycosaminoglycan family along with chondroitin and glucosamine, and works by acting as a cushion and lubricant in the joints and other tissues. HA is an important component of articular cartilage, where it is present as a coat around each cell (chondrocyte).
When cartilage proteins bind to HA in the presence of a link protein, large, highly negatively charged aggregates form. These aggregates retain water and are responsible for the resilience of cartilage (its resistance to compression). In the skin, HA provides moisture that gives it luster and suppleness. On average, a 70 kg (154 lb) person has roughly 15 grams of HA in the body, one-third of which is turned over (degraded and synthesized) every day.