Why don't microwave ovens heat food containers?

Home materials are fine in the microwave and some aren’t (see below). And then there’s plastic. You’ll find experts who say no plastic containers should be used in the microwave—ever. “The material contains chemicals that may leach into food when it’s heated,” says Olga Naidenko, Ph.D., a scientist with the Environmental Working Group, a health-research organization. However, the U.S. Food and Drug Administration (FDA) has deemed that plastics labeled “microwave-safe” are suitable for microwave use. “No studies have shown short- or long-term health consequences from heating microwave-safe plastics,” says Michael Herndon, an FDA spokesman. The bottom line? Right now, there isn’t one. If you choose to use plastics, stick with those labeled “microwave-safe” (but don’t allow plastic wrap to touch your food during heating). If you’re wary, use glass or ceramic dishes marked “heatproof” or “microwave-safe.”