Silicon dioxide (SiO2), also known as silica, is a natural compound made of two of the earth’s most abundant materials: silicon (Si) and oxygen (O2). It’s even found naturally in the tissues of the human body. Though it’s unclear what role it plays, it’s thought to be an essential nutrient our bodies need. Silicon dioxide is also added to many foods and supplements. As a food additive, it serves as an anticaking agent to avoid clumping. In supplements, it’s used to prevent the various powdered ingredients from sticking together.