Hyaluronic acid, is a naturally occurring substance in the body.The largest amounts of it are found in your skin, connective tissue and eyes. Its main function is to retain water to keep your tissues well lubricated and moist.Hydrated skin also reduces the appearance of wrinkles, which may explain why several studies show that supplementing with it can make skin appear smoother. However, the natural aging process and exposure to things like ultraviolet radiation from the sun, tobacco smoke and pollution can decrease its amounts in the skin. When applied to the surface of the skin, hyaluronic acid serums can reduce wrinkles, redness and dermatitis, while firming, tightening, and refreshing the skin.