Cardboard pizza boxes can be recycled, provided they are empty, clean and dry. Remove all inserts and leftover food and cut away any parts of the pizza box containing grease or oil stains. Grease and oil are extremely harmful to the recycling process, even to the point of spoiling entire batches. If you’re unable to remove all the greasy parts of the pizza box, it’s better to play it safe and put the whole thing in the garbage.