Dry skin is caused by a loss of water in the upper layer of the skin. Emollients work by forming an oily layer on the top of the skin that traps water in the skin. Petrolatum, lanolin, mineral oil and dimethicone are common emollients. Humectants, including glycerin, lecithin, and propylene glycol, draw water into the outer layer of skin. Many products also have ingredients that soften the horny substance, keratin, that holds the top layer of skin cells together (e.g., urea, alpha hydroxy acids such as lactic/citric/glycolic acid, and allantoin). This helps the dead skin cells fall off, helps the skin keep in more water, and leaves the skin feeling smoother and softer. Most moisturizers need water to work well. Apply the product after bathing/showering while the skin is still damp. A good skin care product will have a humectant, emollient and a keratin!