Ceramides are fats naturally found in the skin's outer layer, and they make up a major component of skin structure. For this reason, they are crucial for maintaining the skin's natural moisture barrier. "Just like a house is composed of bricks, your skin is made up of cells," says Zeichner. "Ceramides serve as the mortar between the skin cell 'bricks' holding it all together." In fact, studies have linked dry, damaged skin to low ceramide levels [Source: Journal of Investigative Dermatology]. In addition to causing dry, scaly skin, a lack of ceramides makes the skin more susceptible to environmental factors like dirt, pollution and other irritants.