Is It Safe To Use Plastics In Microwave Cooking?

May 12, 2010

By Terry Smiljanich:

Is it dangerous to use plastic containers or plastic wraps in microwave ovens? Are carcinogenic dioxins or other harmful chemicals released into your foods as a result?  There are many frightening claims about this on the internet.  The truth is some caution is advisable in certain circumstances, but all out panic is not necessary.

Microwave ovens heat up your foods by use of electromagnetic waves that heat up the atoms in your food. Heat from a conventional oven does the same thing. It’s just the wavelengths that are different, with microwaves penetrating deeper into the food, thus cooking the food more quickly and efficiently. Any plastics or plastic wraps used in a microwave will likewise heat up, but their particular atomic structures prevent them from heating up as quickly as foods or liquids.

Birth of a Legend

Back in 2002, a news report spread through the internet that a “Doctor Fujimoto from Castle Hospital” in Hawaii had warned of the dangers posed by dioxins in plastics that could cause cancers in people that used such plastics in their microwaves. Emails passed along this warning, and in 2004 information was added that Johns Hopkins Hospital and Walter Reed Army Medical Center were likewise advising of the dangers of dioxins in plastics. In 2007, a “Johns Hopkins Cancer Update” allegedly reiterated this health hazard.

As it turns out, “Dr. Fujimoto” was not a medical doctor or staff physician at Castle Hospital in Hawaii. He was a Ph.D. Director of the Center for Health Promotion at Castle Medical Center in Kailua, Hawaii. Johns Hopkins Hospital in Baltimore did not warn of dioxins in plastics and issued no such “cancer update.” The simple fact is that plastics do not contain dioxins, but the truth can’t easily stop an urban legend from taking off, especially in our connected world.

Bisphenol A

Recently, new internet traffic has warned that plasticizers used in the manufacture of plastics and the presence of Bisphenol A (BPA), can cause cancer or nervous system disorders when used in preparing food. BPA is an industrial chemical used in the manufacture of hard plastic bottles and metal-based food and beverage cans.

The FDA and controlled scientific tests, however, have shown no such adverse effects from normal exposures to BPA. The FDA is continuing the study of BPA’s in foods meant for infants and children (e.g., baby bottles), and is looking for ways to reduce exposure of infants to BPA. In these cases, you would be best advised to stay away from plastic containers containing BPA where children are involved. Check the labeling.

Safe Use of Plastics in Microwaves

So what is the truth about using plastics in your microwave? Any dangers? Well, there are some steps you should take in deciding whether to use plastics in microwave cooking.

Plastics intended for food use must pass FDA safety standards before they are allowed on the market. Since foods may sometimes (but rarely) reach temperatures that melt certain plastics, certain plastic containers are labeled as safe for use in microwave ovens. The biggest danger posed by improper plastics containers is that touching them after heating could cause burns. Butter, for example, often comes in plastic tubs meant for cold storage. Due to its high fat content, butter gets extremely hot in a microwave and could partially melt the tub it is in. The same is true with foods having a high sugar content.

When cooking frozen foods in plastic containers meant to be microwaved, the containers have either been approved for use  by the FDA or tested for compatibility with microwaves.

What About Those Flimsy Plastic Wraps?

Hard plastic containers are one thing, but what about flimsy plastic wraps like Glad Wrap or Saran Wrap? Do they pose a safety hazard in the microwave?

It appears they do not. Using plastic wraps over food helps retain moisture during cooking, thus promoting uniform cooking, and their use also eliminates splattering of food. Microwaves heat the food much more quickly than the wrap. Again, any melting of the wrap is caused by coming into contact with extremely hot food. This is why it is recommended that a small space be maintained between the wrap and the food, especially fatty foods that can get very hot.

Both Glad Wrap and Saran Wrap state that their products are safe for use in a microwave. Glad points out that wraps can tighten during microwaving, and recommends leaving a small vent to allow some steam to escape and prevent splitting of the wrap. Both companies also deny that their products contain BPA or plasticizers.


After posting this article, Consumer Warning Network received an email from Johns Hopkins Kimmel Cancer Center thanking us for writing about the urban legend concerning supposed dioxins in plastic containers. Johns Hopkins still receives daily emails asking whether Johns Hopkins experts had authored such a report, and still encounters bloggers who continue to post the fake report as the truth. The Internet is obviously not always a good source for medical information.