Whether you’re trying to prevent or reverse aging, retinol, a vitamin A derivative, is likely the answer. (The term “retinoid” is the umbrella under which retinol falls, as do stronger, prescription-needed tretinoins, like Retin-A.) Retinol helps skin-cell turnover, so the benefits are numerous: The potent ingredient can do everything from calm breakouts to firm skin to decrease pore size. Side effects can include dryness and increased sun sensitivity (don’t forget the SPF!), and some people report the “retinol uglies,” a period after first usage wherein your skin gets worse before it gets better. (Applying moisturizer before and after application seems to help.) If you can get through that adjustment phase, your patience will likely be rewarded with more youthful skin, whether you’re battling puffy, drooping eyelids, dullness or fine lines. If you have particularly sensitive skin, check with your derm before adding a retinol to your lineup.