Sulfur dioxide might not sound good enough to eat, but this food preservative does make its way into a number of edibles, including dried fruits such as raisins, dried apricots and prunes. Sulfur dioxide is one type of sulfite, a preservative whose name might be more familiar. Even a small amount of sulfite can wreak health havoc if you're sensitive to it. In sensitive individuals, sulfites can cause allergic reactions. These allergic reactions can be relatively mild, such as hives, or more severe -- such as difficulty breathing and potentially fatal anaphylactic shock. For this reason, any food that contains sulfites in a ratio of at least 10 parts per million must include a warning on the label to enable sensitive individuals to avoid these foods.