Hyaluronic acid is a substance that is naturally present in the human & animal body. It is found in the highest concentrations in fluids of the eyes and joints. In humans, the amount in the body is 50% less than optimal by age 40. This is why it is a key ingredient in Recovery Extra Strength. HA is safe as it is naturally occurring in the body and is especially beneficial as we age or if we are under a heavy work load / prone to injury.