"Los Angeles-based esthetician Courtney Chiusano says that she uses this 20% vitamin C serum every morning - and calls it one of her all-time favourite products, too. "it has three forms of stable vitamin C and is a powerhouse at addressing several issues. It refines and tightens the texture of my skin, brightens pigmentation, works wonders on post-acne inflammation, and calms down redness," she says. "This particular serum also has a mild glycolic acid in it, which boosts brightening capabilities and gives skin a nice daily glow. It works great on all skin types and all of my clients love it, but if you are extra sensitive, you can use the 12% version of the serum first."