Microwaving Styrofoam is generally not safe, unless the container has a microwave-safe label. When heated, some styrene can migrate into the food within the container, which can be a cause for concern. This is particularly true for fatty items such as cheese or meat. Styrene is a possible carcinogen, which can pose a threat to your health and reproductive system. Even if there is no visible damage on the foam, a microwave oven may cause the toxic chemical styrene to leach into your food. Therefore, it is best to avoid microwaving Styrofoam containers. If you need to reheat food, transfer it to a microwave-safe container made of glass, ceramic, or plastic.