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Do Microwaves Cause Cancer? (And 3 Other Microwave Myths)

You probably own a microwave. Is it dangerous? Will it cause cancer? Let’s take a look at four microwave myths that science has proven false.

By
Sabrina Stierwalt, PhD
5-minute read
Episode #281
image of a microwave

 

In 1946, an engineer was working near a piece of equipment known as a magnetron which is part of a radar system when he noticed that the radar emission at microwave frequencies melted the snack bar he had stashed in his pocket. Legends disagree as to whether it was a peanut cluster bar or a chocolate one, but the fact remains that rather than just mourning the loss of his snack, he did a little investigating.

He and his coworkers realized that focused beams of microwave emission—that’s waves of energy at frequencies near the radio frequency regime—will cause polar or electrically asymmetric molecules like water in food to rotate. This rotation produces thermal energy (aka heat) which then can quickly and nearly uniformly heat the food.

The microwave was born and dinnertime around the world saw a revolution. The first thing those engineers tried to cook was popcorn. The second thing was an egg which, of course, exploded in their faces. 

Now, according to the US Census Bureau, 97 percent of households in the United States have a microwave. But how much does the average household understand how a microwave works? What misconceptions about our microwave use persist? Let’s take a look at four microwave myths that science has proven false.

Myth #1: Due to the high temperatures, a microwave heats food all the way through to the center

Anyone who has tried to heat a frozen burrito in the microwave knows this myth can’t possibly be true. In fact, the air inside a microwave remains at room temperature, unlike in a conventional oven which takes longer to heat the surrounding air. This air temperature difference is also why your food never comes out of the microwave lightly browned and crispy.

Cold or raw spots in meat that is not already cooked can be unsafe.

The US Department of Agriculture estimates that microwaves only penetrate food down to 1 to 1.5 inches below the surface. Anything thicker than that will have to be heated through conduction of heat from the outer layers of the food toward the center. Thus, cutting that burrito in half at some point in the microwaving process will increase its surface area and allow for more uniform heating.

Microwave cooking does destroy bacteria just as a conventional oven will, but bigger health issues arise when the microwave is used to cook foods like raw meat for the first time and those foods are not heated thoroughly. So while a cold spot in your leftovers can lead to a disappointing lunch, cold or raw spots in meat that is not already cooked can be unsafe.

Myth #2: Microwaving food removes its nutrients

While it is true that some nutrients, like Vitamin C for example, do break down when exposed to heat, this isn’t solely a microwave cooking issue, but rather can occur no matter how that food is heated. In fact, food typically spends less time in a microwave which means there are fewer opportunities for those nutrients to break down. Microwaves can also have the upper hand over other cooking methods because they use less water which is known to leach nutrients out of vegetables, like when they are boiled.

We can’t use the microwave as an excuse not to eat our vegetables—it might be doing an even better job at keeping those nutrients locked in our food!

So we can’t use the microwave as an excuse not to eat our vegetables as it might be doing an even better job at keeping those nutrients locked in our food. In fact, an albeit unsuccessful defamation lawsuit was even brought against the producers of the movie "American Hustle" because Jennifer Lawrence’s character says she read an article by science writer Paul Brodeur claiming that microwave cooking removes nutrients from foods. (Brodeur, not wanting to be associated with the scientifically unsupported argument, was the one who sued for defamation.)

Myth #3: Microwave radiation causes cancer

For some people, the term radiation carries with it a bad reputation when all it means is energy that is emitted by a source. Radiation comes from our bodies in the form of heat. The sunlight that keeps us warm and allows us to navigate the outdoors during the daytime is also radiation.

The forms of radiation that are typically linked to cancer are those with high enough energies or frequencies to ionize—or remove electrons from—atoms or molecules, and thus are able to cause damage in our cells. High energy forms of radiation include X-rays, gamma rays, and some ultraviolet radiation.

The amount of radiation that is allowed to leak out of microwaves based on federal laws in the US is far below the level that could potentially cause harm.

Microwaves, by contrast, are a much lower energy form of radiation. So while they can cause molecules to vibrate, like the water molecules in our leftovers, they do not change the chemical structure of the food by ionizing it or through any other means. Our bodies are full of water and so just as with food, prolonged, intense exposure to microwave radiation will cause those water molecules in our bodies to vibrate and heat up their surroundings. Thus, it is definitely not a great idea to, say, warm yourself up in the microwave if you could fit inside of one.

However, unaltered, properly functioning microwaves do not emit microwaves unless the door is shut. And according to the American Cancer Society, the amount of radiation that is allowed to leak out of microwaves based on federal laws in the US is far below the level that could potentially cause harm. The metal mesh visible through the windows on most microwave doors further have holes that are small enough that the microwaves cannot escape but large enough that visible light can still pass through, or in other words, large enough so that you can still see inside to check on the progress of your lunch.

 

Myth #4: As long as it’s not metal, it can go in the microwave

We know that we can’t put a metal fork in the microwave because metals are great conductors of electricity. The atoms that make up that fork have electrons that are easily freed to move rapidly about the utensil ultimately refusing to let the microwave radiation be absorbed like it is in food. Instead, the microwaves are reflected which can cause electrical sparks between the metal fork and any other nearby conductor of electricity, like the wall of the microwave. These sparks can burn holes in the microwave, cause a fire, and even burn out the microwave.

Until we know more, it may be safest to use a glass container to reheat your food.

But what about plastic containers? Certain plastics that contain lead, BPA (or bisphenol-A, a substance that makes clear, hard plastic), or phthalates (additives that make plastic softer and more flexible) are known for letting these harmful chemicals seep into food when heated. BPA and phthalates are thought to be endocrine disrupters that can upset our hormonal balances and so in the US, plastics containing certain threshold amounts of these materials are not dubbed “microwave safe” by the FDA.

However, in approving something for microwave use, the FDA also considers the surface area ratio of the plastic container to the food, how long the container will sit in the microwave, and how often the container is likely to be used. There also may be other potentially harmful substances or “plasticizers” that turn out to be potentially harmful like BPA but that we have not yet studied. So until we know more, it may be safest to use a glass container to reheat your food.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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