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Can You Microwave Styrofoam (Quick Guide)

Is this common food packaging safe in the microwave?

Claire Onidi By
Claire Onidi
Passionate about food and pastries since always, Claire spends most of her time in the kitchen to develop new recipes. She is French but lived many years abroad.
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Updated June 8, 2022

Styrofoam Takeaway Box
Styrofoam should not be used in the microwave for reheating food, due to potential health concerns.

Instead of using the toaster or oven, it may seem easier to just microwave food right in a styrofoam container. After all, we use styrofoam to keep beverages warm, and to package takeout food.

Made by the Dow Chemical Company, styrofoam, or expanded polystyrene foam, is the trademarked name for extruded polystyrene foam. Polystyrene foam is the same material we use to insulate houses.

So how safe can that be to consume? We’ll look at the health risks associated with polystyrene foam, especially when heated in microwave ovens.

Health Issues Associated With Styrofoam

Styrofoam is found everywhere, from packing peanuts to electronics packaging. It’s prevalently used in the food industry as an insulator, despite its harmful effects on human health.

One of the main components of styrofoam is styrene, which is considered by the National Toxicology Program to be likely carcinogenic. Styrene can leach into food stored in styrofoam, and this is how it ends up in our bodies. (1) Being exposed to styrene can cause side effects such as headaches, dizziness, drowsiness, and fatigue. (2)

If you regularly consume styrofoam packaged foods, you’re at a higher risk of consuming styrene. Be aware of products like styrofoam cartoned eggs, and styrofoam cups. The widespread use of these foam takeout containers should not take away from the fact that they still carry health risks.

Can You Microwave Styrofoam Containers?

No, given the health risks of styrene, microwaving styrofoam isn’t recommended – even if the packaging has a microwave safe symbol.

When styrofoam reaches high temperatures, a process called depolymerization can occur. This is ultimately what causes the material to break down and release styrene. But for this to happen, you would need to heat styrofoam far beyond what’s possible in a standard microwave.

Typical home microwaves have a max temperature of 212°F. The ceiling temperature for depolymerization to happen for styrofoam is 395°F. So, depolymerization is unlikely to happen in your microwave.

Even still, the USDA suggests that food should be removed from its food containers before being microwaved. (3) That’s because materials like plastic and polystyrene containers become unstable at high temperatures and can melt. This melting may cause chemicals in the material to contaminate our food.

How To Safely Reheat Food In a Microwave Oven

  • Always check the packaging of any material you intend to put in the microwave. In general, glass containers like Pyrex and glass-ceramics are safe for microwave use. Paper plates and parchment paper are also safe in the microwave, as long as they don’t contain dyes. According to the FDA, plastic containers are also safe if they have the microwave safe label on them.

  • To reheat foods properly, cover them with a microwave safe container such as a plastic wrap to retain moisture. Leave a corner loose so steam can be released.

  • Microwave cooking also requires a “standing time”, or “carryover cooking time”. Microwaving causes vibrations of 2.5 million times a second, and all that vibrating generates heat. So, your food will continue to cook even after it is removed from the microwave.

  • For best results, let your hot food rest for 1-2 minutes after it comes out of the microwave.

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