Here’s what you should know before reheating those leftovers.
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It’s common knowledge that you should avoid microwaving anything with metal—if you’ve ever accidentally zapped a dish with a scrap of aluminum foil still attached, you know why.

A lot of info out there also warns against the use of microwaving plastic containers, using scary terms like BPA to scare us into transferring our leftovers into a glass dish before reheating them. Yet it gets confusing when you look at items like frozen dinners, which come in plastic containers with specific instructions to reheat them in the microwave. So, what gives?

“In general, any food contact material that is made to transport, package or deliver food to a consumer—including plastic—is regulated by the FDA,” says Tamika D. Sims, PhD, director of food technology communications at International Food Information Council Foundation, an organization focused on communicating science-based information on health, nutrition and food safety to the public.

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The FDA has used toxicological, chemical, and environmental data to evaluate the safety of any food contact material before it reaches the consumer level since 1997, when new procedures were implemented in the FDA’s Modernization Act. So if you toss a package of plastic containers into your shopping cart at the grocery store in anticipation of Thanksgiving leftovers, you don’t have to worry about them containing BPA or other harmful chemicals that could leach into your food.

“What people have to realize is that any food contact substance has already been tested for how much migration is possible,” says Dr. Sims, noting that all food contact substances have some migration properties—even things like frying pans, for example—that aren’t unsafe.

As a rule of thumb, you should pay attention to what the package says, and use any container only as the manufacturer instructs you to do. If it says “do not reuse” or “do not put in dishwasher,” you shouldn’t. But if you break the rule once in a while, it doesn't mean you’re destined for sickness, says Dr. Sims.

The reason manufacturers include instructions like “do not microwave” is because the integrity of the product can start to break down at a certain temperature. While you won’t be causing illness by doing so, you could burn yourself, melt the container, or even harm your microwave. The same holds true for other plastics, like plastic wrap (which begins to break down in the microwave, potentially melting into your food) or plastic cutlery (which can bend and break when it gets too warm).

The bottom line? For things that need a quick reheat, using a plastic container that says it can be microwaved is fine, says Dr. Sims, and you won’t be making yourself sick if you have to heat up your lunch this way every now and then. But if you aren’t pressed for time, it’s worth it to skip the microwave in general and warm up your food in another way.

“Try reheating it with foil in an oven,” says Dr. Sims. “[Doing so] helps things like pizza get crispy, and makes it taste better [than a microwave], too.”