How To Know If Your Takeout Container Is Safe To Microwave

This story begins with a tragic tale of woe: After a long evening at a cocktail party, I returned home with a ravenous appetite for melted cheese. Luckily, I had a plastic takeout container of queso in my fridge, so I stuck it in the microwave and hit the start button. But when I opened the door expecting some bubbly dip ready for tortilla chips, I found that the plastic container had melted and the bottom of my microwave was completely coated in sticky queso.

This grievous situation forced me to reevaluate my takeout reheating habits. When is it OK to put plastic takeout containers in the microwave? What about other materials like Styrofoam and cardboard? (If you’ve ever accidentally microwaved a Chinese takeout container with a metal handle, you probably know the answer on that one.)

Eager for some answers, I reached out to some food scientists, and here’s what they told me about to-go food vessels and how they survive in a microwave.

When microwaved, certain plastics can leach chemicals into the body or break down under the heat.

Had I known more about different types of plastic used to make takeout containers at the time of my queso disaster, I wouldn’t have been as surprised by the sad end result. According to food science consultant Bryan Quoc Le, certain plastics aren’t built to withstand high microwave temperatures. “Polystyrene, polycarbonate and polyvinyl chloride should never be used in the microwave. Polystyrene contains tiny cells of air that rapidly break down in the microwave,” Le explained.

But even if a plastic won’t necessarily melt in the microwave, that doesn’t mean it’s microwave-safe. “Polycarbonate can contain compounds that easily leach into the food after microwaving. While polyvinyl chloride is rarely used in food, microwaving this plastic can release chlorinated compounds,” Le said.

(If you’re wondering how to know what kind of plastic you have, keep reading below.)

Styrofoam can also release chemicals when microwaved.

I remember being told not to microwave Styrofoam food containers as a kid, and an article written by doctors at UCLA Health assures the public that those rules still apply: “Styrofoam is a trademarked name for polystyrene, a petroleum-based chemical compound. It’s manufactured from styrene, a volatile colorless liquid. Studies have linked exposure to styrene to genetic damage to white blood cells and to certain blood cancers. Polystyrene is considered safe for food use when it a solid state. However, heating can cause chemicals to leach from the foam and into the food.”

To figure out whether a plastic container is safe to microwave, always check the symbols on the bottom.

If you’re wondering how you’re supposed to figure out which type of plastic is in your takeout container, the answer can be found on the bottom — just flip it over. “Always check for a ‘microwave safe’ symbol at the bottom of the container to confirm its suitability,” said food scientist and author Jessica Gavin.

While you might see a microwave-safe symbol that looks like a microwave with wavy lines on it, most takeout containers will have stamped numbers on them that will indicate their ability to be microwaved. The numbers you want to see are 2 (high-density polyethylene) and 5 (polypropylene). These materials are the strongest food-safe plastics and can withstand higher heat than food-safe plastics like polyethylene terephthalate (symbol 1), polyvinyl chloride (symbol 3), low-density polyethylene (symbol 4), polystyrene (symbol 6), and other plastics made from mixed resins (symbol 7). Gavin adds that “plastics labeled with recycling numbers 1, 3, 6 and 7 can release harmful chemicals into food when heated.”

Metal and cardboard should never be microwaved because they could potentially catch fire.

Unlike plastic, metal and cardboard aren’t likely to transfer troublesome chemicals into your food. But they can pose a very real risk of setting your microwave on fire.

In a past HuffPost article, Dr. Louis Bloomfield, a professor of physics at the University of Virginia, told us metal “that’s thin is going to cause some trouble.”

“If it’s thin” — as the metal used in takeout containers often is — “it’s likely to get very hot,” he said. That fast and extreme temperature rise can lead to ignition.

As for cardboard, because it’s made of paper that often contains wax or glue, it’s very fire-prone. Also, cardboard containers are sometimes held together with metal staples, which bring another level of chance into the equation.

When in doubt, be sure to transfer your food to a microwave-safe dish.

It may be safe to microwave certain types of takeout containers, but as a general rule, Gavin encouraged us not to take a chance. “Transferring food to a ceramic plate or bowl before heating is a good practice if you’re concerned about chemicals leaching. I always transfer leftovers from to-go containers to a dish before reheating,” she said.