Da real MVPs of the Korean skin care lineup, ampoules and serums deliver high concentrations of actives in formulations made to layer. Unless they work as chemical exfoliants, apply ampoules and serums after any acid, toner, and light essence steps in your routine, then seal in with a moisturizing emulsion and/or cream. Don’t get too hung up on the difference between an ampoule and a serum. Technically, an ampoule is more concentrated and potent than a serum, but in practice, the terms are pretty much interchangeable.