Nearly every modern kitchen has a microwave oven. Since the first domestic Radar Range microwave was introduced 1967, people around the world have been heating up their leftovers, popping their popcorn, and steaming their veggies with the appliance. While it’s become a common commercial and household item, the “science oven” remains a mysterious technology, according to Timothy Jorgensen, an associate professor of radiation medicine at Georgetown University.
“It kind of mystifies people, you know?” Jorgensen said in a recent Science Friday interview. “I think it’s largely because you can’t see it. You can’t smell it. You know it’s there. You see it before your eyes what it’s doing to food.”
And then, of course, there’s the decades-old concern that the humble microwave exposes our food to radiation.
But how dangerous is your microwave, really?
Jorgensen and John Drengenberg, consumer safety director at Underwrites Laboratories (UL), clear the misconceptions, point out the more prevalent hazards, and share tips on how to avoid dangerous mishaps with microwave ovens.
Microwave ovens use radiation, but not nuclear radiation.
One of the most common fears around microwave ovens is radiophobia, or fear of radiation. Jorgensen says that this may be partially due to the fact that the oven produces a man-made type of radiation, said Jorgensen.
“People tend to be more worried about man-made types of radiation rather than cosmic radiation from space or radon from the soil,” Jorgensen said. However, “microwaves don’t have enough energy to cause biological damage as we think x-rays do.”
The world of radiation, Jorgensen further explained, can be divided into two categories: non-ionizing and ionizing.
On the electromagnetic spectrum, ionizing radiation has short wavelengths. The shorter the wavelength, the higher the energy. X-rays, for example, can have wavelengths that are one hundredth of the width of a human hair. Under certain doses and levels of exposure, ionizing radiation could break apart molecules in our body, such as DNA.
X-rays and gamma rays “have wavelengths so short that they can actually rip electrons off of atoms and cause damage, and it’s those things that we worry about,” Jorgensen said.
However, microwaves fall under non-ionizing radiation, which have much longer wavelengths. These types of radiation have energies so low that they can’t break chemical bonds.
Microwaves will not zap the nutrition out of your food.
“The only thing that’s going to destroy food nutrition is if it does get too hot,” said Jorgensen.
If you leave food in the microwave oven for too long, or contents are drying out or boiling over, the nutrition value could decrease. However, you can also make food too hot in an oven or on a grill, Jorgensen pointed out. The waves themselves do not affect the food’s nutrition.
Not all containers are created equal.
Since microwaves heat objects by shaking water molecules, the best containers to hold your food are made of materials that don’t have water. For instance, ceramics and paper plates and bowls allow the waves in easily and don’t have moisture, Jorgensen said.
On the other hand, metals will block the microwaves. Additionally, metal handles on carton take-out boxes, twist ties, and aluminum foil can also create sparks if they graze the sides of the cavity. “We’ve done some research on that at UL, and we can tell you that almost any type of aluminum foil could cause a problem inside a microwave,” said Drengenberg.
Sometimes, metals can be hidden from view, so Drengenberg cautions using certain seemingly innocuous items. A nice set of plates could have a gold or silver trim, and recycled paper plates may have little bits of metal from reconstituted paper, Drengenberg explained.
Watch out! Microwaves get hot, hot, hot.
“You can burn yourself with a microwave oven,” said Jorgensen. “That’s the main hazard with microwave ovens.”
According to the National Fire Protection Association, there is an average of 6,600 fires caused by microwave ovens, with 120 civilian injuries based on 2010 to 2014 annual average data.
“The leading cause of fire inside a microwave oven is popcorn and potatoes.”
During his research at UL, Drengenberg has come across cases where people in a hurry would accidentally heat their food too long—sometimes setting it for multiple hours. Most people often leave the kitchen rather than wait and watch their food while it cooks, said Drengenberg. This could lead to scalds, burns, and even fires.
“The leading cause of fire inside a microwave oven is popcorn and potatoes,” said Drengenberg.
To help prevent fires from spreading, the UL staff set fire to microwave oven designs at their research facilities. They conduct a cavity fire containment test that requires wrapping the appliance with a cheesecloth and cooking multiple potatoes until they become dry and black.
“Then you’ve got a flaming merry-go-round inside,” Drengenberg said. “If that fire inside the microwave oven gets to the cheesecloth, it’s a failure. If it doesn’t, it’s ok. It doesn’t sound too ok when you know that you’ve ruined your microwave oven. But the reality is, it saves your house and it saves your family from a possible terrible disaster.”
Yes, you can stand a safe distance in front of the microwave.
Microwave ovens are designed to keep in radiation. Against the glass, there is a protective mesh screen dotted with tiny holes. These holes are spaced appropriately so that the long microwaves are kept bouncing inside the chamber, while also allowing you to peer through and view your food, explained Jorgensen.
“So you can see through the holes at what’s going on in the oven. But the waves are not actually coming out and cooking you.”
“The waves are not actually coming out and cooking you.”
The team at UL use meters to measure the radiation that may come out of the door or through the ventilation opening, ensuring that the design meets the standard for leakage of microwave energy, Drengenberg said.
Manufacturers build a window on the door so that you can keep a close eye on your food, Drengenberg told SafeBee, UL’s safety blog. However, while there should be almost no radiation escaping from the chamber, it’s best not to press your nose up against the door the entire time your food is heating up. It’s safer to stand on the other side of the kitchen so your exposure is reduced to none, he said.
Beware, the messy microwave oven.
If you spill something in your microwave, clean it up before it seeps into the edge where the door meets the microwave oven, said Drengenberg. Food and liquids that harden and form a crusty mess could create a wedge between the seal of the door allowing microwave energy to escape.
“Keep that door gasket area very clean with a damp rag,” he said. “That’s the best safety device that you have.”
The bottom line: Your microwave is (probably) safe.
The National Fire Protection Association reported that out of the annual average of 166,100 home fires caused by cooking equipment between 2010 and 2014, only 4 percent were caused by microwave ovens. And, only 2 percent of injuries were from microwave oven-related fires.
“Most microwaves today are very good and there are very, very few times that we’ve ever heard of anybody getting burned or hurt from a microwave oven,” said Drengenberg.