Pretty much everyone loves pizza, that is, except for Mother Earth.

An environmentally-friendly pizza lover recently asked the Atlantic’s City Lab if pizza boxes were recyclable. Since they are cardboard, many of us may assume they can can be broken down and reused for paper, insulation — or even more boxes.

But that’s not the case.

Darby Hoover, a resource specialist at the Natural Resources Defense Council, set the record straight on why you should stop dumping pizza boxes into the recycling bin.

Porous paper is “particularly susceptible to food and beverage contamination” and in comparison to other recyclables like cans it “ends up suffering the most from getting mixed with other materials,” she explained to CityLab.

Pizza boxes are tainted by gooey leftover cheese, toppings, and oily stains. The grease from pizza likely soaks into the cardboard—even if you’ve diligently scraped it off. Food and oil cannot be separated from the paper during the pulping process.

There is, however, an alternative for those with access to high-volume composts. Pizza boxes can be tossed in along with other organic waste. But if not, the box, along with any other soiled paper products like napkins and paper towels belong in the trash.

And what about the little plastic tripod used to prevent the pizza from being squished?

Hoover told CityLab that the tripod probably is not recyclable either since it is difficult to tell what type of plastic polymer it is really made of. Not all programs accept all hard plastics—but if yours does, go for it.