Checking the websites of Ziploc and Glad, you learn that the reusable plastic containers made by both companies do not contain cancer-causing BPA. Plus, there is a bevy of BPA-free containers out there to choose from. While that is all very reassuring, what happens when reusable plastic containers are heated in the microwave? To find out the truth,
You might have received an email or heard the rumor that when plastic containers are microwaved, chemicals can leach into your food. According to The Harvard Medical School Family Medical Guide, the FDA "closely regulates plastic containers and materials that come into contact with food. Before approving a container, the FDA conducts tests to make sure that it doesn’t leak unsafe amounts of any substance into food." The FDA conducts tests that measure the migration of chemicals at temperatures they expect the containers to reach with ordinary use. The agency takes into consideration the ratio of plastic to food, how long the container is in the microwave, how often the user will eat straight out of the container, and how hot the container will get. You should know that chemicals do leach out, but in order for a container to be deemed as safe, "the maximum allowable amount is 100 to 1,000 times less per pound of body weight than the amount shown to harm laboratory animals over a lifetime of use."
The American Cancer Society agrees and says that when you heat something up in the microwave, some of the chemicals can seep into your food, but not enough that would be considered harmful. If this sits well with you, then go ahead and keep using those plastic reusable containers in any way you please. But if you're not OK with any amount of chemicals leaching out into your food, I'd go for glass. I think I'll keep using these containers for fruit, veggies, and snacks, but won't be heating them up anymore. I'll save that for Pyrex containers and real plates and bowls.
Remember, all those tests are done with plastic containers specifically designed for microwave use — the FDA doesn't guarantee the safety of microwaving old yogurt or takeout containers.