How Bad Is It Really to Eat Week-Old Leftovers?

Audrey Bruno
Because you've done it before and you'll do it again.

When it comes to leftovers, I'm never sure how long I can eat something before I should probably toss it. In some cases, I've opened up containers of food that I've had for over a week and they've looked (and smelled) totally fine, but I couldn't help feeling a bit uneasy diving in with a fork considering how long they had been sitting there. On the other hand, I've also seen food start to stink and smell after only two days in the fridge.

Leftovers make my life easier for so many reasons—from cutting down my work time in the kitchen to minimizing the amount of food waste I create—but I really, *really* don't want them to get me sick. So I asked food safety experts how to stay on the safer side. It turns out, you can't just look at leftovers and know if they're safe to eat or not, because germs growing on food are often invisible to the naked eye (besides mold, of course). But there are a few things you can do to figure out if you can still eat something or are better off tossing it—plus, some ways to store leftovers to maximize their lifespan.

How long leftovers really last

The FDA says you should typically only keep leftovers in the fridge for up to four days (womp womp), but Randy Worobo, Ph.D., professor of food microbiology at Cornell University, tells SELF that they can potentially last for up to a week depending on how they're handled. (Food stored in the freezer, though, can last indefinitely.)

If you've ever eaten questionably old leftovers and been totally fine, then you should consider yourself lucky. Whether or not you got sick after eating very old food has nothing to do with your "iron stomach" and everything to do with whether or not that food contained bacteria that could cause a foodborne illness, Worobo says. As for the types of pathogens that might be on your food, he says that salmonella, E.coli, and listeria are the most common. If you did eat super old leftovers and didn’t get sick, it’s likely there either weren’t any pathogens on your food, or the amount was simply too small to get you sick. Worobo explains that the amount of microorganisms that will get you sick varies dramatically—for example, norovirus requires one to 10 microorganisms whereas it can take over 100,000 to get infected with salmonella.

So how can you know if your week-old pizza has dangerous bacteria on it or not? You can't, because the pathogens that might get you sick aren't visible to the naked eye, Worobo says. Old food could be dangerous to eat even if it looks totally fine, which is why it's better to use time as a frame of reference if you don't want to take the risk, he says. And, of course, if something *does* have visible mold on it, it's best to throw it out. (Just because something has spoiled or has mold on it doesn’t necessarily mean it’s going to give you a foodborne illness, Worobo says, but it’s better to be safe than sorry in this case.)

I'm going to be totally honest and possibly jinx myself here: I've eaten leftovers that I've had for longer than a week many, *many* times, and I've never gotten sick, so I asked Worobo why that might be. He says that the risk of getting sick from leftovers is actually pretty small, provided you use proper food handling practices (more on that in a bit). If there are no dangerous pathogens on your food, there never will be, unless they are introduced at some point.

“There’s no immaculate conception of bacteria,” he jokes. So as long as you make sure to avoid any cross-contamination and handle food properly so that any existing pathogens can’t multiply to dangerous amounts, he says that leftovers can last up to a week in some cases. After that point, though, it's no longer worth the risk, especially for very young children, elderly adults, people with autoimmune conditions, pregnant women, people with conditions like diabetes and HIV/AIDS, and those undergoing treatment for cancer, he says, because they’re more likely to get sick from a much smaller amount of bacteria.

One exception to this rule is seafood, says Philip Tierno, Ph.D., clinical professor in the departments of microbiology and pathology at NYU Langone Medical Center. "Generally speaking, the most contaminated food product is seafood and it breaks down easily and quickly," he explains. "Fish with an odor is being broken down and bacteria are increasing in population." Anyone who's eaten seafood knows how quickly it can go from smelling delicious to smelling sour, and the FDA doesn't recommend holding onto any fresh seafood leftovers for more than one to two days (smoked fish, on the other hand, will be fine for up to 14 if packaged in an airtight container).

If you're wondering why it seems like cooked leftovers don't last as long in your fridge as the raw ingredients do, it's because they don't, says Worobo. Bacteria develops more quickly in cooked food for a handful of reasons. "Microorganisms need water, the proper temperature, and the proper acidity [to multiply]," he explains, "so if you take a cake mix and add water and eggs, you’re supplying the nutrients for the pathogens.”

How to keep your leftovers as fresh and safe as possible

Listen, leftovers are delicious and convenient, so you want to make sure you’re doing what you can to keep them fresh and safe to eat as long as possible. Here are a few ways you can do that:

First, make sure to never leave leftovers at room temperature for more than two hours. After that, food runs the risk of entering the danger temperature zone—between 40 and 140 degrees F—which is an environment that allows microbes to grow much faster, says Tierno. And if you're in a particularly hot place, he says you shouldn't leave leftovers out for longer than an hour before transferring them to the fridge (and make sure your fridge is cooled to just below 40 degrees F, which is what it should typically be set at). If you can't get leftovers to a fridge before that amount of time has passed—maybe because you're out for the day and carrying it around in your bag—he says it's safest to simply throw them away.

This two-hour rule is the main reason why it can be riskier to save leftovers from a restaurant than food you cook at home, says Worobo. The longer food is kept at room temperature the more likely it is to develop potentially dangerous bacteria, and if you're at a restaurant or ordering delivery, you may not be able to get food in the fridge quickly enough. However, if you are able to refrigerate them within two hours, and the restaurant that they come from uses proper food handling practices, your risks are pretty much the same as they would be with homemade food, says Worobo. "But if the restaurant has poor practices, the chances of getting sick are higher," he explains. Unfortunately, you can’t always see what’s going on back there in the kitchen, so there’s always going to be a certain amount of unknown risk involved when you eat out.

There's also no danger in keeping leftovers in the original takeout containers, but they will probably last longer and retain their flavor and texture better if transferred to something airtight, says Worobo.

Despite what you may have heard, it's totally fine to put leftovers in the fridge while they're still warm. Tierno says that it's common for people to leave leftovers out at room temperature until they cool down completely, but that this is a mistake. The longer food spends at room temperature, the more opportunity there is for bacteria to grow, he explains. Instead, Tierno says it's better to transfer leftovers straight to the fridge even if they're still warm. He says the temperature of the food will drop much faster this way—usually in just an hour. The hot food may briefly warm up the temperature of your fridge, but he says it should cool back down in no time, and it won't ever get warm enough in there to put your other food in harm's way. Place containers in the fridge with some space around them, if possible, to increase circulation of cool air.

But first, transfer food to smaller, airtight container to speed up cool down time. In case you haven't noticed, cooling down leftovers as fast as possible is key to keeping them safe to eat. "If you’re putting a gallon container in the fridge it’s going to take more than a day to cool down enough, and the pathogens can be growing actively that whole time," Worobo explains. Instead, he suggests facilitating the cool-down process by packing food in small, shallow containers, and leaving them uncovered in the fridge with plenty of space, if possible, to increase circulation. Cover everything up once it's had a chance to fully cool, preferably with an airtight lid to keep food fresher for longer.

Be careful to avoid cross-contaminating your food. Cross-contamination is one of the biggest mistakes consumers make when packing up leftovers, says Worobo. (This is how safe food sans pathogens can end up dangerous.) Be extra sure that you're not scooping with spoons that have touched raw food that potentially could be contaminated (like poultry). Instead, always use clean storage vessels and serving spoons to guarantee no pathogens are reintroduced to already-cooked food.

Label everything so you know exactly how long you've had it. Tierno says that everything you put in the fridge should get labelled so that you know exactly how long you've had it for. As mentioned before, many potentially dangerous microbes are invisible to the naked eye, so something may look fine when it's actually not. If you don't date your food, you could wind up eating something that seems OK but isn't. Save yourself the stress by marking containers with the date you stored them.

Make sure your fridge is at the right temperature. According to Worobo, your fridge should be kept at 40 to 45 degrees F at all times to guarantee the quality of your food, but most consumers have their refrigerators at 50 degrees F and don't even realize it. If your leftovers have been getting you sick lately, it might have something to do with how cold (or not) your fridge might be. To ensure your fridge isn't too warm, he recommends investing in a fridge thermometer like this one if it isn't already equipped with one.

Before eating leftovers, heat them to 165 degrees. "Proper reheating can protect you from the pathogens you can’t see with your naked eye," Worobo explains. If there are any pathogens present on your food, heating them to this temperature will kill them off, he says. This is especially important to do if you’re approaching that one-week mark. According to the FDA, leftovers should be heated to at least 165 degrees F to ensure they're safe to eat. Unfortunately there’s no good way to eyeball when your food is at the right temperature, so Worobo says it’s best to always make sure with a thermometer.

For best results, the FDA suggests covering leftovers with a microwave-safe lid or plastic wrap, making sure there's some sort of small vent for steam to escape, and rotating the food halfway through (and give it a stir, while you're at it). The more evenly the dish heats up, the better chance you'll get every inch to the right temp so that it's safe to eat.

Of course, not all leftovers are meant to be eaten hot, like leftover chicken salad, for example. In that case, it’s even more important to eat or toss within three or four days, says Worobo.

All products featured on SELF are independently selected by our editors. If you buy something through our retail links, we may earn an affiliate commission.

Related:

Originally Appeared on Self