Are you microwaving with unsafe food containers? You wouldnt put metal or aluminum foil in your microwave because it could damage the oven. You should not use a plastic container that wasnt designed to be microwaved, either. It will not hurt the oven, but it could possible hurt your health. Heat is the big issue. Plastics designed for the microwave can stand up to high heat - the 170 or 180 degrees necessary to kill bacteria in food. Less sturdy plastics, like margarine tubs and leftover deli containers, can blister, warp or start to melt under heat as low as 120 degrees. The FDA imposes stringent regulations on plastic containers meant for microwaving. Research is not conclusive, however, about the potential danger (if any) posed. Just remember leftover food should always be reheated to 165 degrees F to kill any bacteria. So keep this in mind when reheating leftovers. Stir or rotate food midway through the microwaving time to eliminate cold spots where harmful bacteria can survive. Occasional use is not believed to be of concern. Its the constant use of the same plastics over time that could be harmful. So when microwaving, remember to make it hot, but play it safe.