Getting Cancer From Your Tupperware: Is that re-heated meatloaf putting you at risk? Probably not. Maybe you heard the stories of chemicals leeching out of plastic containers and into your food when you put them in the microwave. While it's true that some plastics contain dangerous chemicals, the ones meant for heating food generally do not. This is why they're designed for... heating food. Rocket science, we know. That said, look for the words "microwave safe" on the label. And be wary of take-out containers from groceries and restaurants however. They're often meant for one use only.