Many people assume that pizza boxes are recyclable. In fact, most boxes have recycling symbols on them and are traditionally made from corrugated cardboard. They are, in and of themselves, recyclable.
However, what makes parts of them non-recyclable is the grease and cheese from pizza that soil the cardboard. Pizza boxes that are tarnished with food, or any paper product that is stained with grease or food, are not recyclable – unless you remove the tainted portions.