This resource helps familiarize you with the types of vitamin C found in skincare products. While serums with the active form of vitamin C, L-ascorbic acid, are considered the "gold standard," they're usually very acidic, often irritating, and notoriously unstable. So you might consider one of the many vitamin C derivatives instead. Most of them will gently deliver similar benefits, and offer a much longer shelf life. With this cheat sheet, you'll be able to identify vitamin C in ingredients lists and make an informed choice about which type to use in your routine.