Glycerin is a humectant, a type of moisturizing agent that pulls water into the outer layer of your skin from deeper levels of your skin and the air.. In skin care products, glycerin is commonly used with occlusives, another type of moisturizing agent, to trap the moisture it draws into the skin. When applied topically, humectants can attract water from deeper skin layers and from the environment around you. Glycerin also helps slow the evaporation of water from your skin, which is why it’s frequently found in moisturizers and serums, as well as in cleansers which can dry out the skin as they get their job done.