Microwaving Styrofoam can cause chemicals to leech into your food — here's why you should use glass instead

• Avoid microwaving Styrofoam, or EPS, as chemicals in EPS leach out faster when exposed to heat.
• Microwaving EPS containers can also cause them to crack or break.
• Opt for microwave-safe glass containers instead of ones made of EPS.

Microwaving those takeout containers from last night might seem like a convenient option for lunch. However, zapping Styrofoam may come with health and safety risks, says Rolf Halden, professor and director of the Biodesign Center for Environmental Health Engineering at Arizona State University.

The concerns involved with microwaving Styrofoam are two-fold. For one, the microwaving process can leach chemicals into food. It can also compromise the container's structural integrity, causing hot food to spill inside the microwave or onto you when removing the container.

What is EPS?

"Styrofoam is a trademarked brand name for an insulation material and building product made from extruded polystyrene foam," says Halden. It's not used to make coffee cups or takeout food containers, but people favor the term regardless.

White packaged food containers or expanded polystyrene (EPS) foams are plastics made from tiny beads that are heated and molded into a specific shape, adds Halden.

In addition to being bad for the environment, EPS also poses a potential health risk since chemicals can leach from the containers into food and drink — whether you microwave them or not.

Why you shouldn't microwave EPS

Microwaving speeds up the chemical leaching process. "Heat can generate more free chemical building blocks, and it also accelerates their movement out of the plastic and into the food," says Halden. Heat from the microwave stresses the material, which can crack and fragment, releasing pieces into your food. More heat translates to more chemicals being released into your food or drink.

The U.S. Department of Health and Human Services (DHHS) has listed styrene, a chemical in EPS, as a "reasonably anticipated human carcinogen." When these small polystyrene particles end up in your body through ingestion, the chemicals can bind to certain receptors causing hormone-like activity, Halden explains. Because of the potential associated health risks, some states, such as Maine, have introduced legislation to ban the use of specific EPS foam products like food containers.

Putting EPS in the microwave can also compromise a container's structural integrity by melting the foam causing food or drink to spill, potentially causing burns.

Microwaving Styrofoam containers one time isn't likely to cause any immediate health issues, though, but exposure can add up over time. "If you pull a hair from your scalp once, it's inconsequential. If you repeat that several times day in day out, you are creating a visible problem," explains Halden.

Quick tip: Most recycling centers can't recycle Styrofoam. Contact your local waste office to find out whether they can handle Styrofoam. Don't try to reuse Styrofoam food containers. There's no way to sanitize them safely, and the nooks and crannies in the porous materials are a breeding ground for bacteria.

Safe ways to heat food in the microwave

The good news is that you can avoid chemical exposure by using alternative options for heating food in the microwave, says Halden.

Instead of reheating food inside an EPS container, Halden recommends transferring food or drinks to a microwave-safe container made of glass. The FDA also lists microwave-safe plastic and ceramic as suitable choices for microwaving.

Look for a microwave-safe symbol on the bottom of your container to see if it's ok to microwave. This will usually be a microwave with wavy lines.

Quick tip: Keep in mind that some glass containers come with lids that are not microwave-safe. Bamboo food container lids, for example, should not go in the microwave.

Insider's takeaway

Avoid heating containers made of expanded polystyrene (EPS). Microwaving EPS can leach chemicals into your food and potentially negatively affect your health. Heating EPS in this way can also cause it to break, spilling food and causing burns in the process. Using microwave-friendly, reusable containers like ones made of glass is the safest way to reheat food in the microwave.