Some plastic food containers are not formulated to withstand the effects of being heated in a microwave oven. The United States Department of Agriculture Food Safety and Inspection Service warns that such containers can melt or warp in the heat. Additionally, the USDA says various kinds of harmful chemicals can end up in your food if you put a non-microwave-safe plastic container in a microwave.
This article was found in Livestrong.Com. To obtain more information, go to http://www.livestrong.com/article/173172-what-are-the-dangers-of-plastic-food-storage-containers/