Eartha: Use the precautionary principle when microwaving plastics |

Eartha: Use the precautionary principle when microwaving plastics

Dear Eartha,

What plastics are safe to put in the microwave?

— Susan, Silverthorne

Bottom line is that if you subscribe to the precautionary principle, it’s probably best to avoid microwaving plastic as much as possible since there are still so many unknowns. The easiest solution, when you can’t use “real” dishes, is to use glassware.

Great question, Susan. This topic recently arose in our household as well. I have avoided putting plastic food containers in the microwave for years, but I’ve heard that many plastic containers are now safe to microwave.

The Food and Drug Administration is responsible for testing plastic containers that come into contact with food. The agency considers the ratio of plastic surface area to food, how long the container may be in the microwave, how often someone may eat from the container and how hot the food may get during microwaving. It then measures the plastic chemicals that leach out of the container into the food. Based on the results of the testing, plastic containers can earn a microwave-safe rating from the FDA. Some containers, like frozen meals, are rated for a one-time microwave use. Importantly, many plastic to-go containers and kids melamine plates are not safe to use in the microwave.

If the FDA is rating microwave safety of plastics, then what’s the issue? Many scientists still aren’t sure whether using plastics in the microwave is completely safe. The “better safe than sorry” approach, more eloquently known as the precautionary principle, is rarely used by the U.S. government. The precautionary principle implies that in the absence of scientific consensus, the burden of proof that something is not harmful falls on product manufacturers.

So what are the specific chemicals that may adversely affect us if we microwave our food in microwave-safe containers? There are three chemicals that have raised red flags among scientists: bisphenol A (BPA), estrogenic chemicals similar to BPA, and phthalates.

BPA is often found in rigid plastics, often with the #7 symbol, and is used in some of the more durable plastic food containers. You may recall BPA began getting a lot of bad press around 2008. We were urged to stop drinking or eating from any plastics containing BPA. Microwaving food or letting beverages sit in these containers was especially egregious. My son was born in 2006 and it was impossible to find BPA-free bottles. We ended up using glass bottles, which worked just fine and were more impervious to breaking than you’d think.

In 2012 and ’13, the FDA banned BPA from baby bottles, sippy cups and infant formula. These bans came after manufacturers had already removed BPA from most of these products. Despite the bans, BPA is still widely used in the U.S., including in plastic food containers, to-go packaging and as a lining in many canned food products. According the FDA, “BPA is safe at the current levels occurring in foods. Based on the FDA’s ongoing safety review of scientific evidence, the available information continues to support the safety of BPA for the currently approved uses in food containers and packaging.” The FDA continues to study BPA and acknowledges that human health effects of BPA are not known, but that BPA does affect the reproductive systems of laboratory animals.

BPA is an endocrine disruptor, mimicking estrogen in humans and animals. Estrogen is important in bone growth, ovulation and heart function. Some potential health impacts of BPA ingestion include early puberty, increased breast cancer risk in women, obesity and diabetes. Unfortunately, the chemicals that have replaced BPA in rigid plastic food and beverage containers are also estrogen-like. So a BPA-free product is not necessarily safe.

The other class of chemicals to be wary of is phthalates, which are used to make #3 PVC plastic more pliable. Phthalates are also present in lotions, shampoos and other personal care products. Like BPA, studies show that Americans, especially infants and children, have phthalates in their urine. Phthalates are linked to developmental delays in children, and certain phthalates may be endocrine disruptors.

One plastic we haven’t addressed is #5 polypropylene, which is used in many plastic food containers. Polypropylene appears to be safer than the aforementioned plastics, though I have seen partially dissolved surfaces after microwaving food.

Bottom line is that if you subscribe to the precautionary principle, it’s probably best to avoid microwaving plastic as much as possible since there are still so many unknowns. The easiest solution, when you can’t use “real” dishes, is to use glassware. Pyrex has a great line of food containers and lids that works well for home storage and to-go meals.

And for drinks, stainless steel or glass continue to rule in the safety arena. By doing a little planning ahead and having glass or stainless containers, you can easily avoid any health concerns associated with plastic.

Ask Eartha Steward is written by the staff at the High Country Conservation Center, a nonprofit organization dedicated to waste reduction and resource conservation. Submit questions to Eartha at

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