Pronounced "dye-METH-i-kone", this ingredient may be found in many skin care, makeup and hair care products. Manufacturers use it in moisturizers, primers and foundations because it helps fill in uneven texture and fine lines, creating a smooth, flawless look. "Dimethicone is the main ingredient in most oil-free moisturizers," says Joshua Zeichner, M.D., director of cosmetic and clinical research at Mount Sinai Medical Center in New York City. "It's a light emollient that forms a protective layer over the skin's surface, helping to hydrate and keep moisture in." Emollients, like petrolatum, lanolin, and mineral oil, soften and moisturize the skin and can also decrease flaking [Source: WebMD]. They do this by creating an oily layer on top of the skin that traps water.