Glycerin

Glycerin, sometimes labeled glycerol or glycerine, is a humectant, meaning it draws water in and helps skin hold onto it. It occurs naturally in every fat molecule, whether the fat comes from a plant or an animal, and can be produced by breaking fats down or fermenting sugar. Most skincare brands, however, rely on a synthetically made version, since that process yields a purer ingredient.

What makes glycerin notable is that it's already a substance your skin produces on its own to help regulate hydration. Because of that, it's classified as a replenishing ingredient rather than an outside addition, and it plays a central role in defending skin against dryness and keeping moisture levels balanced. On its own, glycerin is an excellent hydrator, but it works even better paired with emollients and other moisture replenishing ingredients that soften and smooth skin.