You should not put a Styrofoam takeout box in the microwave. Takeout containers are typically made from expanded polystyrene foam (EPS), a type of plastic not designed to withstand the high temperatures generated during microwave reheating. While the U.S. Food and Drug Administration (FDA) considers polystyrene safe for holding hot and cold food, this applies only to its intended use, not to exposure to intense, rapid microwave heat. If a foam container is safe for microwaving, it will have a specific “microwave-safe” symbol, usually an icon of a microwave with wavy lines, but most standard takeout containers lack this designation.
The Physical Danger: Melting and Warping
The physical risk of microwaving a standard foam container stems from the material’s low heat tolerance. Expanded polystyrene foam begins to soften and lose its structural integrity at temperatures far below the boiling point of water. Since microwave ovens heat the food, the container is exposed to heat conducted directly from the hot contents, which easily exceeds the foam’s softening point.
This exposure causes the container to warp, deform, or even melt, leading to a loss of shape and potential spillage of hot food. The structural failure creates a burn hazard for the person handling the leftovers. Additionally, melted plastic residue can adhere to the microwave’s interior, requiring difficult cleaning and potentially damaging the appliance.
The Chemical Danger: Leaching into Food
Beyond the physical breakdown, heating polystyrene foam introduces a chemical risk to the food inside. The material is manufactured using styrene, which can migrate, or leach, out of the container and into the meal when heated. This leaching is accelerated by microwave heat, especially with fatty foods like meats and cheeses.
Styrene is classified by the U.S. Department of Health and Human Services as a “reasonably anticipated human carcinogen.” The heat increases the amount of this chemical that transfers to the food. Some research also suggests that chemicals released from heated polystyrene can act as endocrine disruptors, interfering with the body’s hormonal systems.
Safe Alternatives for Reheating Takeout
To avoid the risks of melting and chemical leaching, transfer your leftovers to a different container before reheating. Glass and ceramic dishes are excellent choices because they are inert, meaning they do not react with food or release chemicals when heated. These materials withstand high temperatures without warping or degrading, making them ideal for microwave use.
For foods that benefit from a crisp texture, such as fried items or pizza, the oven or a toaster oven is a better alternative. Place these items on a baking sheet and heat them at a moderate temperature, around 350°F, until warmed through. Sauces, soups, and stir-fries can be effectively reheated on the stovetop in a pot or skillet, which allows for better temperature control and even heating.