Should You Microwave Plastics?

Aug. 16, 2007 — -- Am I standing too close? How much time does that need? Will this explode?

For such a common household appliance, microwaves seem to provoke an uncommon number of questions. For many people, the inner workings of their microwave oven remain a mystery -- and, of course, what can and can't be nuked has long been a subject of discussion.

One of the more furious debates centers on the many different plastic containers that people use in the kitchen. Are plastics safe to microwave?

Physicist Michael Bloomfield, who writes about microwaves in his book "How Things Work," says the answer isn't simple. "Some plastics are safe. Others you might think twice about."

First of all, Bloomfield explains, many types of plastic are not made to withstand high temperatures. While you obviously wouldn't place a takeout container over an open flame, you might pop it into the microwave without thinking twice. But the plastic is being exposed to heat there as well, Bloomfield said.

Although the microwave isn't actively warming the plastic, foods -- especially those rich in sugar or fats -- can easily reach temperatures that certain containers can't tolerate. "You can easily take something right out of the deli, put it in the microwave, and end up shrink-wrapping … your food," he warned.

All Plastics Aren't Created Equal

While the safest route is to use plastic containers clearly marked "microwave safe," Bloomfield said you can also judge for yourself with translucent containers. The cloudiness is a giveaway. "Microscopically [a cloudy] plastic has a crystalline structure in it," he explained. "This will hold its strength at microwave temperatures."

So double check with transparent plastics as they are most likely to melt, and be careful with colored or opaque plastics because they might be weaker plastic mixed with dye, he said.

If something melts in the microwave, at least it's obvious. But what if plastic is getting into your food and you can't see it?

Jeannie Wang, a mother in New York City, worried that she might be putting her child at risk by reheating meals in plastic containers, even "microwave safe" containers. "It's just really convenient for me to put plastic in the microwave," she said. "But then I've heard from some sources that this might not be safe because there are chemicals that can leach into the food."

Playing It Safe

It's true that microwaves cause chemicals to leach out of plastic containers and into your food. There are scientists who say some of these chemicals may be harmful -- even at low levels. The Food and Drug Administration says plastic with a "microwave safe" label is thoroughly tested for food safety and that the amount of chemicals that might leach into your food from these approved containers isn't dangerous.

One of the most controversial plastic chemicals is bisphenol A, or BPA, found in hard clear plastics like baby bottles. Last week, a federal panel recommended more research to address some concern about infants and children being exposed to this chemical.

Despite the FDA's reassurances, some people choose to avoid microwaving plastics altogether.

Barbara Kafka is the author of "Microwave Gourmet" and uses her microwave to prepare meals you might expect from a fully staffed kitchen -- dishes like shrimp and pea risotto or chicken liver and ground pork pate. She prefers to cook with other materials. "I use china and glass containers in the microwave," she said. And while she recognizes that microwaving plastics might be harmless, she prefers to play it safe. "It's just easier not to do it, and why should I?" she asked.

But Kafka emphasized that people's confusion over the safety of containers should not scare them away from microwaves.

"I want people to not be afraid to cook in the microwave oven -- to actually cook," she said, adding that during the long summer days many people avoid the hot kitchen. "If you can't stand the heat, get out of the kitchen," She laughed. "No, can't stand the heat, use your microwave!"