For Your Safety, Never Put These Things In The Microwave

Although the microwave has saved a lot of time, many people have voiced concerns about its safety. Microwaves shoot electromagnetic radiation into food to heat it. Unfortunately, many items don’t respond well to that radiation.

Certain foods may explode in the microwave. Even mostly safe materials, such as styrofoam, may start a house fire if you warm up the wrong variety. Before you put objects into the most common kitchen appliance, learn what isn’t safe, clean, or practical to warm up in the microwave.

Aluminum Foil

Aluminum foil is wrapped around a pie crust.
Denver Post Photo by Cyrus McCrimmon
Denver Post Photo by Cyrus McCrimmon

Microwaving aluminum foil is a recipe for a fire hazard. The small electric fields spark through the foil, which may catch fire. Never put a large amount of aluminum foil in a microwave.

According to the USDA, it’s safe to put a small amount of aluminum foil in the microwave to “shield” parts of food from heat. But don’t cover more than 1/4 of the food, and make sure your foil isn’t wrinkled. Creases in foil can cause arcing, which creates sparks.

Food With Shells (Mainly Eggs)

Four brown eggs site on a table; one is broken open.
BSIP/Universal Images Group via Getty Images
BSIP/Universal Images Group via Getty Images

Food with shells–including eggs, nuts, and seeds–will not survive the microwave. The heat builds up steam faster than the shells can ventilate it. Eventually, the food may explode. In April 2019, an English woman was sent to the hospital after a boiling egg exploded in her face.

Some sites advise people to prick the shell so that the steam can escape. However, the English woman did that, and her egg still exploded. Your safest bet is to keep shelled food away from the microwave, period.

Some Plastic Bags And Wraps

Soup is held in plastic containers covered in plastic wrap.
ilovebutter/Flickr
ilovebutter/Flickr

According to Dr. Russ Hauser, the Harvard chair of the Department of Environmental Health, plastic can be made from different materials. Depending on the type of plastic used, a bag or wrap may not be microwave-safe. Fortunately, the FDA requires manufacturers to test their plastic in the microwave.

The danger of plastic is that the chemicals could leak into your food. Because of that, Dr. Hauser recommends not heating plastic in the microwave. If you use plastic wrap, don’t let it touch your food. And don’t warm zip-locking bags, either.

Carrots And Other Vegetables

A person pours olive oil onto a pan of carrots to roast.
Anne Cusack/Los Angeles Times via Getty Images
Anne Cusack/Los Angeles Times via Getty Images

If you research methods about steaming vegetables, you’ll see plenty of tutorials on how to microwave carrots. But over the past couple of years, reports have emerged of carrots that caught on fire. And it’s not just carrots; kale, bell peppers, and green beans have also sparked. According to the USDA, this is called arcing.

Arcing is when the microwave’s electric field turns into sparks. High-nutrient vegetables can intensify the electricity. Plus, the vegetables’ shape may also conduct electricity. Cook your carrots on the stovetop or oven instead.

Frozen Meat

Packages of meat are frozen.
Sergei MalgavkoTASS via Getty Images
Sergei MalgavkoTASS via Getty Images

Although defrosting meat in the microwave won’t damage your kitchen, it may create a health hazard. According to the USDA, microwaving meat puts it close to the “danger zone.” That’s the temperature zone in which bacteria multiplies, between 40°F and 140°F. Only microwave meat if you’re going to cook it right afterward.

If you want to microwave meat before cooking, follow these tips from Health Canada. First, remove all packaging and transfer the meat to a microwave-safe container. Use a bowl or deep dish to contain the juices. Wrap it loosely with plastic wrap that doesn’t touch the meat, and leave an opening.

Cheap Glazed Ceramics

A woman enjoys hot chocolate in a Christmas ceramic mug.
Andrew Michael/Education Images/Universal Images Group via Getty Images
Andrew Michael/Education Images/Universal Images Group via Getty Images

If you buy ceramics from a reliable manufacturer, they’re safe to microwave. However, beware of ceramics made in China. The country does not regulate the industry well, so the products may not be microwavable. Check the label before heating it up.

If you don’t know how safe the container is, try a water test. Pour water into the container and warm it for 30 seconds. If the container is hotter than the water, then it’s not safe to microwave. If the water is hotter, try it again for another minute.

Dry Or Wet Sponges

A person wearing gloves washes a dish with a sponge.
Stefan Klein/ullstein bild via Getty Images
Stefan Klein/ullstein bild via Getty Images

According to an internet cleaning tip, microwaving a wet sponge will kill the germs on it. But it won’t. A study in Scientific Reports says that microwaving a sponge may actually make the bacteria worse. The heat may kill some pathogens, but the worst bacteria will remain on the sponge–and multiply.

Bacteria thrive in warm, moist environments, like a wet sponge in a microwave. Heating a dry sponge is even worse; it could catch on fire. If your sponge gets dirty, throw it out and replace it.

Grapes

grapes in microwave
@SueanoiM/Twitter
@SueanoiM/Twitter

Want hot grapes? We’re not sure why you would, but don’t microwave grapes. In 2011, YouTubers captured grapes that caught on fire in the microwave. According to physicists, the fiery blob is actually a loose pile of electrons called plasma. Grapes are the perfect size for amplifying microwave electricity.

As cool as this sounds, it’s still not safe to conduct microwave experiments on grapes. You’ll still get a ball of hot molten plasma in your microwave that could set your kitchen on fire. If you’re curious, watch YouTube videos about it.

Some Styrofoam Products

A styrofoam container holds leftovers from restaurants.
Marvin Joseph/The Washington Post via Getty Images
Richard Baker / In Pictures via Getty Images Images

Contrary to popular belief, most styrofoam containers are microwave-safe. But not all of them are. Most takeout containers are not microwave-safe if they hold creams like mustard or butter. Don’t heat foods high in fat, like ramen or soup, in styrofoam containers.

Always read the instructions before heating up styrofoam. If a takeout container says “one-time use only,” don’t microwave it. If you can warm up styrofoam, open the lid a bit to allow your food to vent. And don’t keep heating after it boils.

Nothing

A microwave oven is open.
Illustré/RDB/ullstein bild via Getty Images
Doris Thomas/Fairfax Media via Getty Images

Don’t turn on an empty microwave. Although it may seem harmless, it can break the machine. With nothing to heat up, the microwaves will automatically go to the magnetron tube, which also supplies the energy source. If that goes on too long, it’ll damage your microwave, say experts at the University of Illinois.

Some people discover this when they run their microwave accidentally. If you set a timer on your microwave, make sure that it isn’t heating up. A couple of seconds won’t damage it, but a couple of minutes might.

Twist Ties

A black twist tie rests in someone's palm.
Andréanne Germain/Flickr
Andréanne Germain/Flickr

Never heat twist ties in a microwave. These ties are shaped with a small metal wire and covered in craft paper. The tiny bit of metal guides electrical currents that can burn, especially if that metal is twisted.

Twist ties show that metal doesn’t have to be big to harm your microwave. If the metal twists or wrinkles, it can cause a fire. Before heating up a container or wrapper, check it for any small bits of metal. However, staples in tea bags are safe.

Containers With Metal Handles

A Chinese takeout container has metal handles.
@Mizztien/Twitter
@Mizztien/Twitter

The USDA lists all safe and unsafe metals for microwaving. Unfortunately, most takeout containers don’t adhere to the safety requirements list. Boxes with small metal handles should not be microwaved because they can burn the paper and start a fire.

Before microwaving a takeout container, remove the handles. Most paper is safe to warm up without the metal. When heating up food, never pair metal with paper, as that’s a recipe for a house fire. You can always transfer the food before warming it.

Dishes With A Metal Trim

A 20th-century white bowl has a copper rim.
The Museum of East Asian Art/Heritage Images/Getty Images
The Museum of East Asian Art/Heritage Images/Getty Images

If your dish, cup, or bowl has a metal trim, don’t microwave it. This includes dinnerware with gold, which was not designed to withstand high heat. The metal may overheat and create tiny sparks that will damage your microwave and dishware.

Most retailers who make silver, copper, or golden-laden dishes do not make them microwave-safe. But some newer versions have been built to handle microwaves. Always read the label before warming it up. When in doubt, don’t warm it up–better safe than sorry.

Stainless Steel Travel Mugs

A woman holds a white travel mug.
@timothyeberly/Unsplash
@timothyeberly/Unsplash

If your travel mug is made with stainless steel, don’t heat it in the microwave. The steel reflects heat and electricity, which could bounce back at your microwave and damage it. In the worst-case scenario, the steel may spark and catch fire.

Even if your stainless steel mug has a ceramic lining, it still isn’t microwave-safe. In the best-case scenario, it won’t even heat up your coffee. Since the metal deflects warmth, you’ll end up with a cold drink and burning hot mug.

Hot Peppers

Colorful hot peppers are on display at a market.
Joan Slatkin/Education Images/Universal Images Group via Getty Images
Joan Slatkin/Education Images/Universal Images Group via Getty Images

Never warm peppers such as jalapenos, habaneros, or chilis in the microwave. No, it won’t harm your kitchen, but it could injure you. The electric waves may release capsaicin, the active compound that gives peppers their spice. Then, the microwaves’ fan may disperse the capsaicin, essentially pepper-spraying you.

The USDA adds that some vegetables can spark in the microwave, such as peppers. Experts believe that the minerals used to grow these vegetables may cause arcing. If your vegetable sparks, remove the part that was electrified.

Bread

A person holds slices of bread.
Artyom GeodakyanTASS via Getty Images
Artyom GeodakyanTASS via Getty Images

People warm bread in a toaster for a reason. It’s not just for the crunch; a microwave will ruin your bread. After ten seconds, all the moisture will leave the bread. That’s enough to leave a stale, dry, chewy mess. Not what you want from toast.

Although you can’t toast bread in a microwave, you can bake or proof bread in a microwave. Most recipes combine a short microwave segment along with oven baking. Don’t try to microwave a bread loaf from scratch.

Some Types Of Paper

Popcorn pours out of a brown paper bag.
Julia Ewan/TWP CAPTION/Getty Images
Julia Ewan/TWP CAPTION/Getty Images

Not all paper is microwave-safe, according to International Microwave Power Institute president Bob Schiffmann. For instance, brown paper bags are never safe in the microwave. Since they can’t handle a lot of heat, they may catch fire. Newspaper and any other paper with ink may leech into your food and contaminate it.

Wax paper, parchment paper, napkins, and paper towels are safe for the microwave. So are paper bowls and plates. Don’t warm up dirty paper because that can spread germs to the rest of your food.

Baby Formula Or Breast Milk

A woman checks the price beside a shelf of Dumex baby formula
STR/AFP via Getty Images
STR/AFP via Getty Images

The FDA does not recommend microwaving breast milk or baby formula. Although baby milk is best served lukewarm, the microwave does not heat it evenly. When some parts are warmer than others, the hotter portions could scorch a baby’s mouth.

You can microwave baby food, but you must do it correctly. Don’t heat the food in a jar; transfer it to a microwave-safe dish. Heat it for a bit, stir it, and then heat it again for an even temperature. Always taste test microwaved food before feeding it to your baby.

Oils

A woman pours olive oil into a bowl.
David Silverman/Getty Images
Franco Origlia/Getty Images

If you want warm oil, you won’t get that from a microwave. It’s not dangerous; it’s just a waste of time. Cooking oils don’t have the molecule polarity that water has. According to a 1998 study, a microwave can change olive oil’s chemical structure, but it won’t warm it up.

Butter can melt in the microwave because of its fat content. But defrosting butter in the microwave won’t work well. The ice makes heat oscillation difficult, so you’re better off defrosting butter in the fridge.

Clothes

Clothes are folded on a bed.
Getty Images
Getty Images

Some people think that heating their wet clothes in the microwave will dry them. It won’t–at least, not as well as a dryer. The microwave will heat water molecules outside and inside the fibers. If you warm the clothes for too long, it may catch on fire.

Plus, there is nowhere for the steam to go in a microwave. You may end up with damp clothes that are still wet in certain areas. Hanging them to dry for a day is far easier and safer.