According to the US Food and Drug Administration, melamine's chemical migration problem becomes more significant in the presence of acidic foods. Heating melamine-ware containing acidic food, such as tomato sauce, orange juice or vinegar, to temperatures higher than 160 degrees Fahrenheit causes increased chemical migration and potential health effects. Leaving acidic materials in melamine containers for a long period of time also could cause problems.
Microwaving non-microwave-safe plastics, including melamine, can damage the plastic material, as well as causing potential health risks. Microwaved plastic may warp, melt or bubble. Melamine softens in heat, making it a poor choice in the microwave and as a stirring utensil for hot foods. Keep melamine tableware cool, and use it only for serving and storage.