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Everyday Health
Are Microwave Ovens Safe or Harmful?
By By Leanna Coy, FNP-BC. Medically Reviewed by Justin Laube, MD,
2 days ago
Microwave ovens aren't inherently dangerous, but you do need to know how to use them safely. Adobe Stock; Everyday Health
Yes, microwave ovens can be dangerous, but maybe not for the reasons you think.
Microwaves have used radiation to heat foods in American kitchens for decades and for just as long, some people have worried that microwave ovens pose health risks and may even refuse to eat food that has been heated in a microwave.
Our experts weigh in on legitimate concerns about microwave ovens, and some unfounded fears you don't have to worry about.
What Are the Negative Effects of Microwaves?
Because microwaves use a kind of technology that involves radiation, some have worried the ovens are dangerous. But microwaves don't use the type of radiation that leads to radiation sickness.
Instead, microwave ovens heat food using electromagnetic "micro" waves that cause water molecules within the food to vibrate. This vibration generates heat that warms the food.
The energy from a microwave could heat body tissues in the same way it heats food, by vibrating molecules. But for this to happen, a person would have to be inside a microwave oven with the door closed, an unlikely occurrence given the size of a typical microwave. If it were to happen, tissues in the body containing water and those closest to the radiation generate the most heat. This heating may cause burns to the skin or cataracts in the eyes.
Raheem Hashmani is a researcher in high energy physics at the University of Wisconsin in Madison. He says, "the only problem with microwaves would be if you repeatedly exposed yourself to a microwave source, you start to heat up. But this is no different from standing very close to an open flame."
Is It Harmful to Stand Near a Microwave?
Provided the door is properly sealed, "it isn't harmful at all," says Hashmani. The electromagnetic waves in microwaves belong to a form of radiation called "non-ionizing" radiation. Non-ionizing radiation is not radioactive like the ionizing radiation used in X-rays or nuclear power. According to the National Cancer Institute, "Non-ionizing radiation includes visible, infrared, and ultraviolet light; microwaves; radio waves; and radiofrequency energy from cell phones. Most types of non-ionizing radiation have not been found to cause cancer." The microwave's design keeps radiation inside the oven and blocks the microwaves when the oven is off and the door is open. If the microwave is working properly and undamaged, the risk of radiation exposure is about zero. To reduce potential exposure, the FDA recommends consumers avoid standing directly in front of the microwave or pressing against it while it is running.
Can Microwaves Leak Radiation?
Microwave ovens have built-in safety features to keep them from producing energy when the door opens. "When you close the microwave door it acts like a little cage, otherwise known as a Faraday cage," says Hashmani. The interior metal walls of the microwave act as mirrors, causing the electromagnetic waves to bounce around inside. Doors that don't close correctly because they're dirty, have broken seals, or other visible damage increase the potential for leaks. To reduce the threat of radiation exposure:
Never use a microwave if the door doesn't close properly.
Do not use if the seal around the door is broken.
Keep the door seals clean.
Are Microwaves 100 Percent Safe?
Hashmani acknowledges that manufacturing defects that result in cracks or gaps may allow electromagnetic waves to leak. But, he says, "The microwaves are far too weak to be dangerous."
You cannot see or smell microwave energy, making it hard to detect any problems with a faulty machine. Hashmani has a hack to uncover potential leaks from the microwave: He says electromagnetic microwaves and Wi-Fi signal frequencies are very close. If the Wi-Fi signal on your phone drops when you turn on the microwave, this may indicate a leak.
The use of plastic in a microwave remains problematic. Plastic containers that store cold foods, like margarine or yogurt, will cause chemicals to release into foods during microwave cooking. The creation of microwavable food plastic containers (MFPCs) tried to reduce this risk. But one recent study showed that MFPCs have some of the same problems and allow microplastics to leach into food during heating. Evidence shows microplastics cause negative health effects in the body. This means that a safe plastic may not exist for microwave use.
"I'm not a fan of heating food in plastic," says Jeff Culbertson, PhD, a retired emeritus professor of food science and technology at the Ohio State University, food science and technology. He agrees that even MFPCs can leach into foods, especially when new; the amount leaching decreases with each use. He recommends breaking in new plastic containers by filling them with water and running them through a few cooking cycles to allow the polymers to pull out of the plastic into the water.
"Then the plastic might be a lot safer," he says. Dr. Culbertson recommends using only rigid plastic when cooking in a microwave. "Use the same rigid plastic container over and over again. Never use a plastic bag."
Effects of Microwave Cooking on Nutrients
Microwaved foods contain the same nutrients as foods cooked with other methods. Evidence indicates the vibrating water molecules used in microwave cooking may preserve nutrients.
Culbertson says, "There is no doubt that microwaves preserve nutrients more efficiently than any of the other methods." He says the heating methods used for steaming, baking, and air frying destroy more nutrients by heating foods from the outside in.
Heat-sensitive nutrients are the exception, Culbertson says. He identifies thiamine (B1) and vitamin C as the most sensitive. He says that in the United States, however, we generally overconsume thiamine by eating fortified grain products, and foods high in vitamin C aren't usually microwaved.
Carcinogens in Microwaved Food
It is a myth that microwaved foods cause cancer. According to Hashmani, the electromagnetic waves are too weak. "They can't ionize any of the material in your skin or your body. All they can do is vibrate and cause it to heat up."
The non-ionizing radiation used in microwave cooking is not radioactive. The radiation stops when the cooking stops. No radiation is left behind, and none stays in the food.
Does Microwave Cooking Kill Bacteria?
Safely cooking foods requires heating them thoroughly to destroy bacteria. Undercooked food may cause foodborne illnesses . Researchers have shown that microwave ovens destroy bacteria just like other methods of cooking without affecting the quality of food. On the other hand, thicker or denser foods do not heat evenly in the microwave and some portions may remain undercooked. Always make sure food has cooked completely to destroy any bacteria present.
Culbertson also points out, "We don't really kill a lot of microorganisms when we're reheating food in a microwave." Most people heat foods just to the point where the food is a good temperature for consumption and don't get it hot enough to kill off bacteria that grew while the food was cooling down after the first use.
"The food isn't going to taste as good if you microwave it multiple times. It's also not exactly a safe process from a food safety standpoint," he says. Stirring or rotating foods halfway through the warming cycle will help reduce cold spots where bacteria may survive.
How to Avoid ‘Superheating' Burns
When water boils at 212 degrees F, the boiling action releases air bubbles, allowing steam to escape the fluid but microwaving water does not cause this same boiling action. Instead, superheated hot spots above the 212 degree F boiling point build up an inch or two under the surface. When the hot spots are disturbed by adding a tea bag, powder, or, in rare cases, just moving the liquid, an eruption can occur causing the hot spot to boil over. At those temperatures, liquids will cause burns on skin. Foods may cause burns as well. Various foods respond differently to microwaving based on their makeup. Foods with non-porous surfaces (like processed meats) or foods with different layers of structure (such as eggs with yolks and whites) will heat unevenly. This may lead to the risk, albeit uncommon, of exploding foods. To reduce the risk of superheating injuries, take precautions:
Stir every so often while heating liquids.
Add a tea bag or a small amount of the powder to liquids at the beginning of the heating process.
Don't heat liquids longer than the recommended time.
Use a container with sloped walls.
The Takeaway
Our two experts agree that microwave ovens cook food efficiently without harming it. "In general it's one of the least destructive ways of cooking food," says Culbertson.
Concerns about microwaves causing cancer are unfounded, but heating food in plastic containers can lead to chemical leaching. While microwaves preserve nutrients well, they can heat food unevenly, potentially leading to foodborne illnesses if they're not used correctly.
Microwave ovens use non-ionizing radiation, which does not pose the same risks as ionizing radiation and is safe when the microwave is undamaged and properly used.
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy . We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Díaz-Galiano FJ et al. Cooking Food in Microwavable Plastic Containers: In Situ Formation of a New Chemical Substance and Increased Migration of Polypropylene Polymers. Food Chemistry . August 15, 2023.
Deng X et al. Insight Into the Incredible Effects of Microwave Heating: Driving Changes in the Structure, Properties and Functions of Macromolecular Nutrients in Novel Food. Frontiers in Nutrition . October 13, 2022.
Osaili TM et al. Inactivation of Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in Tahini by Microwave Heating. Foods . December 2, 2021.
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