There is a green halogen light. There is a revolving glass plate. There are a few seconds to a few minutes of humming that end in a loud beep. Over 90 percent of American families use microwaves to heat food in a hurry.
Do microwaves emit radiation? Yes but increased distance reduces the amount of radiation exposure significantly. And continuous exposure to the radiation microwaves emit is a real health risk, and it is important to mitigate that risk with appropriate shielding.
We’ll dig into the details more in this article.
How Do Microwave Ovens Work?
Microwave ovens work by generating intermolecular friction.
It’s the same principle as rubbing your hands together to get them warm. When you rub your hands together, the friction between your two hands jostles the cells in your skin.
Your cells are held in place by ceramides and adhesive tissues, so they become agitated but they can’t transform the energy from rubbing your hands together into motion. That friction energy becomes heat, which, along with increased circulation, makes your hands warmer.
A microwave generates magnetic energy. That magnetic energy also tugs on molecules that are held in place by the non-magnetic molecules around them. Water, it turns out, is very weakly magnetic. The water inside food is also jostled around but trapped within the structure of your food. Water heats up as your microwave generates magnetic energy and steams your food from the inside out.
Microwave ovens are practical for everyday use because water is only weakly magnetic. As you may have discovered, highly magnetic materials and microwaves don’t get along very well. The metal lined napkin I set over the bread to reheat in the microwave before Thanksgiving dinner last year can confirm this.
The force of gravity may hold a piece of metal down until the agitated atoms inside generate enough heat that it explodes in a flash.
And sometimes even weakly magnetic objects, like a baking potato with an unusually high water content, will generate enough motion that they levitate inside your microwave.
(Don’t try this at home. Any potato and any other object that has a composition that can cause it to float in mid-air when it’s put in your microwave can also explode in your microwave.)
Radiofrequency (RF) Radiation
How does a microwave generate the magnetic field that causes the intermolecular friction that turns into heat to cook or reheat our food?
Microwave ovens use a modern version of the magnetron that melted Percy Spencer’s peanut bar and popped popcorn for everyone in his office.
A magnetron is a high-powered vacuum tube.
When you turn on your microwave, electricity flows into an elongated, perfectly centered metallic cylinder in the middle of the tube called a cathode. The cathode is made from a material like barium oxide that releases electrons into the vacuum around it.
Around the cathode there is a ring of metal called the anode block. The anode block is made of a highly conductive metal such as copper. Cavities are drilled into this ring of metal so the whole apparatus generates resonant frequencies that amplify the magnetic energy generated by the flow of electrons from the cathode to the anode across the vacuum.
The interaction of the two parts of the magnetron generates waves of radiofrequency radiation (RF radiation) at just the right frequency to activate water molecules to generate heat.
How Much Radiation Does A Microwave Emit?
The honest answer to the question of how much radiation does a microwave emit is “It depends.”
Obviously, microwave ovens generate enough RF to melt butter, boil water, and heat up frozen dinners.
The magnetrons inside most microwave ovens generate between 600 and 1200 watts of energy in the form of RF radiation.
In scientific terms, that means the oven generates between 600 and 1200 joules of energy every second.
“OK,” you and I might ask, “what’s a joule?” That’s the amount of energy needed to move a mass of 1 kilogram one meter. One watt of energy generates joule every second.
Or, to put the explanation in relatable terms, if all the energy generated by your microwave were then absorbed by your food and converted into motion rather than heat, your microwave could throw a 2-pound potato two miles through a vacuum in two seconds. Fun fact!
That is, if it didn’t explode first, and it would. Or if we had vacuum tubes two miles long for two-pound potatoes, and we don’t.
Fortunately, the process of microwaving food doesn’t operate at theoretical efficiencies. The magnetron inside your microwave is engineered to emit radiation in a limited range of frequencies.
Only a small part of the RF spectrum agitates water molecules. And those water molecules are held inside the structure of food that doesn’t respond to those frequencies. Even when a microwave oven is in operation, RF is only one of many physical forces at work.
Still, one has to wonder if Percy Sidney and his peanut bar weren’t just somehow lucky. Can it really be safe to stand next to a microwave oven? Should we really have one in the house?
Let’s start with the question of whether it is safe to stand in front of microwave ovens while they are in operation.
Is It Safe to Stand in Front of Microwave Ovens?
When Percy Sidney accidentally invented the microwave, people were still tying little bags of radium to necklaces to prevent cancer.
Luckily, the general understanding of the dangers of radiation of all kinds has greatly improved since the 1940s. The Center for Devices and Radiological Health, which is part of the Food and Drug Administration, has specific standards for shielding microwaves so they don’t emit radiation.
We’ll discuss those in more detail in a moment. First let’s consider the kind of radiation emitted by a microwave oven.
RF radiation emitted by a microwave oven is non-ionizing radiation.
This means that isn’t at a frequency that changes the chemical structure of, for instance, DNA. It’s not like gamma radiation from nuclear bombs and supernovas. And it doesn’t generate a stream of charged particles like alpha radiation.
The effects of RF radiation are through the generation of heat, and they are most noticeable in the parts of the body that cannot conduct heat away from themselves, such as the eyes.
However, prolonged exposure to RF radiation can cause measurable health problems. Let’s look at some of the evidence for health challenges resulting from exposure to RF radiation from cell phones:
- The International Agency for Research on Cancer (IARC) did a kind of review of research studies on RF and cancer called a meta-analysis in 2011. They compiled data across a series of research studies that showed that RF is a possible human carcinogen. It’s not possible to do a clinical trial in which some participants might be exposed to the risk of cancer to prove that RF causes cancer. But experiments in the laboratory with animals exposed to a lifetime’s worth of radiation from cell phones showed increased risk of one kind of brain cancer (glioma) and a kind of benign tumor that covers nerve cells (schwannoma).
- Both experiments and case studies confirm that men who carry cell phones in their pants pockets have greater risk of a condition called asthenozoospermia. This is an inability to produce sperm that lacks “swimming ability” that is defined as the inability of sperm to travel forward at a rate of at least 5 millimeters per hour. produce sperm that is not fully formed or that has deficient “swimming ability.” Men who carry cell phones in their pants pockets who already have a genetic predisposition to infertility may also develop macrozoospermia, a condition in which they develop excessively large heads and cannot fertilize the ovum.
- There is special concern about children’s use of cell phones. The radiation from any cell phone a child holds penetrates more deeply into the growing brain because of the size of a child’s head. At least one study has found that increased social interaction more than compensates for any brain damage from cell phones, but one has to wonder if increased social interaction increases a child’s speech and learning abilities, can’t children interact without cell phone
Getting Back To Microwaves
What does all this have to do with the radiation from microwave ovens?
Here is the connection: The Center for Devices and Radiological Health requires cell phones to be shielded so they emit no more RF radiation than 1.6 watts per square centimeter when they are held at the ear.
But the Center for Devices and Radiological Health only requires microwave ovens to emit no more than 5.0 watts per square centimeter at a distance of 5 centimeters (about 2 inches) from the oven door.
If you stand at your microwave oven door eagerly observing your next meal being cooked, you are getting more than three times the dose of radiation that studies have found to be a problem with cell phones.
But does that mean microwave radiation is harmful?
Is Microwave Oven Radiation Harmful?
There is a simple solution to avoiding harmful radiation from your microwave.
Don’t spend long periods standing with your nose up to the window of your microwave peering in.
If your face is two inches away from your microwave’s window while it is in operation, your body is receiving three times as much RF radiation as it does when your cell phone is on.
If your face is three inches away from your microwave’s window while it is in operation, your body is receiving the same amount of RF radiation as it does when your cell phone is on.
And if you stand back from your microwave six feet away while it is in operation, your body receives 0.00000000000000000002 percent (that’s 19 zeros) as much radiation as when your face is just two inches away from the viewing window.
So, microwaves are safe and we don’t need to worry about radiation?
Well, almost. Microwaves are safe at a distance when they are properly shielded up to government regulations.
To be safe, double check that your microwave is properly sealed so additional radiation isn’t leaking out when it’s in use. According to the Canadian Centre for Occupational Health and Safety, old or faulty door seals are the most common causes of microwave oven radiation leakage.
I break out my EMF meter every now and again to be sure I’m not noticing any spikes in the readings (this one from Amazon is the meter I use).
Most microwave ovens are safe to operate as long as you don’t press your nose against the glass to watch your food cooking. And with appropriate microwave radiation shielding you can use them every day without worry.
How the Microwave was Invented
In 1946, an engineer named Percy Spencer was assigned the task of making military radar more powerful. As his grandson tells the story, Spencer had a soft spot in his heart for feeding squirrels. He always carried a peanut cluster bar in his pocket to break up and feed the squirrels at lunch. One day Spencer was testing a military grade magnetron in his lab when he suddenly noticed that the peanut cluster bar in his pocket had melted.
Curious about what the heck had just happened, the next day Spencer brought an egg to work. He placed it by the magnetometer. A few minutes later, it exploded in his face.
There it was. The first microwave.
More RF radiation articles you might be interested in:
The Amazing True Story of How the Microwave Was Invented by Accident. Popular Mechanics. 2016
Mobile phones electromagnetic radiation and NAD+-dependent isocitrate dehydrogenase as a mitochondrial marker in asthenozoospermia. Biochimie Open. 2016. Authors: Abeer M.Hagras Eman A.Toraih Manal S.Fawzy
De Braekeleer, M., Nguyen, M. H., Morel, F., & Perrin, A. (2015). Genetic aspects of monomorphic teratozoospermia: a review. Journal of assisted reproduction and genetics, 32(4), 615–623. https://doi.org/10.1007/s10815-015-0433-2
Papadopoulou, E., Haugen, M., Schjølberg, S., Magnus, P., Brunborg, G., Vrijheid, M., & Alexander, J. (2017). Maternal cell phone use in early pregnancy and child’s language, communication and motor skills at 3 and 5 years: the Norwegian mother and child cohort study (MoBa). BMC public health, 17(1), 685. https://doi.org/10.1186/s12889-017-4672-2