Skin hydration: a review on its molecular mechanisms.

Glycerin naturally exists in your skin's outer layer (stratum corneum) where it acts as a humectant—basically a water-magnet that helps your skin hold onto moisture. Your skin relies on two things to stay hydrated: glycerin and similar natural moisturizers inside skin cells, plus a lipid barrier that prevents water from escaping. When this system breaks down, you get the visible dry, flaky skin that no amount of moisturizer can fix.