Pizza can spoil if you leave it out for too long, just like any other perishable food. Food safety experts say you’re relatively unlikely to get sick from eating a plain cheese or pepperoni pizza that’s been sitting out for hours or even a day. However, it’s more likely to be a problem if there are juicy toppings, like tomatoes or buffalo chicken. Plus, your pizza is more likely to dry out and get stale if you don’t refrigerate it.