Tooth decay is the breakdown of tooth structure which results in cavities. Tooth decay can affect both the enamel (the outer coating of the tooth) and the dentin (the inner layer of the tooth). Tooth decay occurs when foods containing carbohydrates (sugars and starches) such as breads, cereals, milk, soda, fruits, cakes, or candy are retained on the teeth for a long time. Bacterial flora in the mouth digests these foods, turning them into acids. The bacteria, acid, food debris, and saliva combine to form plaque, which clings to the teeth. The acids in plaque dissolve the enamel surface of the teeth, creating holes in the teeth called cavities, or caries.