Studies show that glycyrrhizic acid, an ingredient in licorice, stops the cold sore virus cells dead in their tracks -- so try chewing a licorice whip. Just be sure it's made from real licorice, as most "licorice" candy in the United States today is flavored with anise. If the ingredient list reads "licorice mass," the product contains real licorice. You could also try buying some licorice powder and sprinkling it on the sore, or mix up a cream with a pinch of licorice power and a smidgen of pure vegetable shortening, then apply to the sore. Remember, though -- don't go overboard! Just as with any medicine, real licorice's medicinal effects can cause serious side effects if used in large amounts over long periods of time.