Hyaluronic Acid (HA) is the cushiony substance found throughout the body, which keeps joints supple and skin plump-and yes, like everything else it diminishes with age. Babies are born with a high level of HA, but with age, most significantly after 40 it faded away. "It's like a sister to collagen," Gross says, "But whereas you can stimulate collagen production, you can't really stimulate hyaluronic acid production-you can only replenish it." Derms love HA due to it's unsurpassed ability to hydrate and add volume, it can hold up to 1000 times it's weight in water. HA's only downside is it's large molecule size that hindered absorption, but new formulas penetrate deeper and are ultra plumping. Not the newest or most hip ingredient out there, HA is tried and truly good for hydration and younger looking skin. Applied topically it not only improves hydration and elasticity, but also free radical damage. And an added bonus, HA is appropriate for all skin types.