Using Plastics in a Microwave: Safe or Risky?

By Carol Johnson

The U.S. Food and Drug Administration has received inquiries from concerned consumers for years asking about the dangers of heating food in microwaves using plastic containers. Horror stories abound on the Internet about people contracting dreaded diseases because of chemicals leaching out of plastic into food while it’s being heated in a microwave.

Some of those stories may have been of concern decades ago, when both microwaves and plastics were less technologically advanced as they are today. But nowadays, consumers can be confident that the FDA carefully reviews all substances used to make plastics designed for food use. Such items include microwave-safe containers that hold frozen dinners, plastic ware for cooking in microwaves, and microwave-safe plastic coverings that keep food from splattering. Even microwaveable popcorn bags contain a metalized plastic film that lets them reach the high temperatures required for the corn to pop fully.

Edward Machuga, a consumer safety officer in the FDA’s Center for Food Safety and Applied Nutrition, says that consumers should be aware that substances used to make plastics can indeed leach into food. "But as part of the approval process," Machuga said, "The FDA considers the amount of a substance expected to migrate into food and the toxicological concerns about the particular chemical."

One chemical that has received a lot of attention in the media is called diethylhexyl adipate (DEHA), a substance added to some plastics to make them flexible. DEHA exposure may happen when foods wrapped in plastics—especially fatty foods such as meats and cheeses—are heated in a microwave. However, the levels of DEHA that might leach into the food are very low, so the levels that might be consumed as a result are well below toxic levels.

The FDA has evaluated migration levels of substances added to regulated plastic materials and has found the levels to be well within the margin of safety according to their guidelines and research study information. As new scientific information is discovered, the FDA revisits its safety evaluations to be sure consumers are protected.

Under the food additive provisions of the Federal Food, Drug, and Cosmetic Act, any substances used to make plastics for food use must be found safe for their intended use before they can be sold to consumers. Such substances, called "food contact substances," are what researchers test for to determine toxic levels and decide whether plastic items are microwave-safe.

Claims that plastics contain dioxins have been successfully countered by FDA researchers. Dioxins are a group of contaminants labeled as "likely human carcinogens" by the Environmental Protection Agency. But Machuga says, "The FDA has seen no evidence that plastic containers or films contain dioxins and knows of no reason why they would."

The FDA recommends that consumers use plastics only for their intended purpose and in accordance with directions provided by the manufacturer. If you don’t see instructions on a plastic item for microwave use, you should assume that the item is not microwave-safe and instead use a different plate or container. For example, plastic takeout containers from restaurants, margarine containers, and other inappropriate containers may melt or warp when food is heated in them in a microwave. Microwaveable meal cartons are intended to be used only once, and should be discarded after being used.

Microwave-safe plastic wrap must be placed loosely over food so that steam can escape, and it should not touch the food directly. "Some plastic wraps have labels indicating that there should be a one-inch or greater space between the plastic and the food during microwave heating," Machuga says. Generally, microwave-safe plastic wraps, wax paper, parchment paper, and white microwave-safe paper towels are okay to use. But never use plastic storage bags, grocery bags, or aluminum foil in the microwave.

As with most food-related items, it’s better to err on the side of caution than to risk getting sick or injured. So if your neighbor brings you some homemade soup in a nice white plastic bowl and you’re not absolutely sure it’s microwave-safe, you’d be better off putting it in a bowl before heating it.