Is It Safe to Eat Pizza That's Been Left Out Overnight?

Eating pizza that sat out all night is a lot like falling asleep without taking your contacts out or brushing your teeth—three things that can go hand-in-hand after a long night out on the town. We all know it's probably not a great idea, but just how bad is it to eat the leftover pizza? Can it really be that ill-advised if we made it through our 20s with no horrific bouts of food poisoning? To find out, I checked with food safety experts from the USDA and the Cleveland Clinic.

Is It Safe to Eat Pizza That Sat at Room Temperature for Hours?

Let's cut to the chase: "It's not safe to eat pizza that's been left out overnight," says Carly Sedlacek, RD, a registered dietitian from Cleveland Clinic's Center for Human Nutrition. "Pizza is considered a perishable food and if left out can cause bacteria to grow and lead to possible foodborne illnesses such as [those caused by] Staphylococcus aureus, E. coli and Campylobacter," Sedlacek adds. "Bacteria often grows on food when it's in the 'Danger Zone,' which is between 40°F and 140°F. Perishable foods need to be kept at 40°F or below." That means food needs to go in your fridge.

Like other perishable foods, pizza that has been at room temperature—or anywhere in the 40°F to 140°F danger zone— for more than two hours should not be consumed, confirms Meredith Carothers, a food safety specialist with the USDA's Food Safety and Inspection Service. In addition, if the temperature is above 90°F, perishable food should not sit out for more than an hour, per the USDA.

What Are the Dangers of Eating Pizza That Sat Out Overnight?

Any bacteria that are present on your leftover pizza grow rapidly in that danger zone between 40°F and 140°F, and can double in number in as little as 20 minutes, Carothers says. That means you're vastly increasing your risk of being exposed to foodborne pathogens—and possibly coming down with a foodborne illness—if you dig into that slice sitting on the counter when you wake up.

What Symptoms Should I Look Out For? What Should I Do If I Get Sick?

Be on the lookout for gastrointestinal symptoms, including cramping, stomach pain, diarrhea, nausea and vomiting, as well as fever. "The onset of symptoms may occur within minutes to weeks and often presents itself as flu-like symptoms," says Carothers. "Because the symptoms are often flu-like, many people may not recognize that the illness is caused by harmful bacteria or other pathogens in food."

While many instances of food poisoning resolve on their own, if you have symptoms that are severe or last more than 24 hours, you should seek medical attention. Further, children, pregnant women, older adults and those with weakened immune systems are at higher risk from foodborne illness and should get medical attention immediately if food poisoning is suspected, according to the USDA.

But I've Eaten Pizza That Sat Out and I Didn't Get Sick—Why?

I asked the experts how is it that so many people got through college eating leftover pizza that sat out, if it's so dangerous. "Many individuals may choose to indulge in pizza that's been sitting out overnight and not get sick," Sedlacek concedes. "However, while we're not able to see the bacteria that may grow on food that sits out, it does not mean it's not there and can put you at risk for foodborne illnesses." Ultimately, you probably just got lucky if you ate pizza that sat out and felt fine.

What About a Meatless or Vegan Pizza? Can I Eat That If It Sat Out?

Sorry to say, the same food safety rules apply no matter what kind of pizza you left out. "The safe period for different kinds of pizza does not vary," says Sedlacek. "If the pizza contains cheese and meat, or if you're enjoying a vegetarian or vegan pizza, both contain perishable items that can collect bacteria if not stored properly."

OK, I'm Convinced. Now How Do I Store My Pizza Safely?

Sedlacek says to place your leftover pizza in an airtight container or wrap it tightly and then get it into the fridge. Leftovers, including pizza, can be kept in the fridge for three to four days, according to the USDA. You can also freeze pizza—it'll be safe indefinitely but for the best flavor and texture, try to eat it within three months. Thaw leftovers in the fridge, not on the counter, to avoid providing a breeding ground for bacteria, says Sedlacek, citing USDA food safety guidelines. Sedlacek and the USDA also recommend aiming for an internal temperature of 165°F when reheating food to ensure food safety.