glycerin is the most frequently used cosmeticingredient documented through the FDA’s VoluntaryCosmetic Reporting Program. Glycerin is a well-known humectant that prevents the premature loss of moisture fromcosmetics and personal care products so they don’t dry out.
propylene glycol is a humectant (hydrating) and delivery ingredient used in cosmetics. In cosmetics, propylene glycol is used in small amounts to keep products from melting in high heat or from freezing. It also helps active ingredients penetrate skin.