Is it Safe to Eat Leftover Pizza?

After you cook food, you put it in the fridge to keep it safe. Right? So what about yesterday’s pizza that’s still sitting in its box on the kitchen counter? Good news: a food safety expert tells us that day-old cheese pizza is “low risk.”

Now, he can’t guarantee that it won’t kill you. But Benjamin Chapman, food safety specialist at North Carolina State University, says that people don’t end up getting sick from unrefrigerated pizza often enough for it to be an issue on public health radar.

Why not? “It all comes down to water activity,” Chapman says. Bread and baked cheese are both too dry to be friendly to germs. Tomato sauce has some moisture, but its acidity probably keeps bacteria in check.

Toppings change the calculus, though. If you order your pizza with nice juicy diced tomatoes on top, that’s one that should go in the fridge. I asked Chapman about other toppings on the juicy-to-dry spectrum. Pepperoni is fine (it’s often sold at room temperature, anyway) but what about green peppers? Buffalo chicken? They’re fine if enough water got baked out of them. So how can you, average home pizza-eater, know if that’s the case? Bad news: “You can’t.”

So you’re on your own for this judgment call, but it sounds like plain and pepperoni pizzas are unlikely to kill you. Good luck if you decide to take your chances with the rest.