There’s no doubt that a good microwave can make life so much easier. The problem? When used incorrectly, microwaves can be quite dangerous. “Many Americans don’t realize that between 2009 and 2013, cooking within the home was the leading cause of house fires according to the National Fire Protection Association (NFPA), says Chandler Coleman, a consumer insights investigator for ConsumerSafety.org. “And one of the biggest cooking hazards is the microwave.”
As it turns out, I know this firsthand. When I was about eight years old, a friend put polymer clay in our microwave. The details are hazy at this point, but in a matter of minutes, our house was filled with smoke and the fire department was on site.
According to Ginger Davis Allman of The Blue Bottle Tree, this happened because microwaves don’t heat evenly. The things you microwave can “superheat, melt, and actually bubble and boil, while other parts [can] expand and ooze out.” After just a few minutes, the overheated parts can start to burn—which is what happened with the clay.
In my case, we were lucky—my parents’ home was unharmed, and we escaped with just a gentle scolding. But since then, I’ve always been extra careful about what goes in my microwave, and what should never go into it, like the below.
“Styrofoam is not only bad for the environment, but is extremely toxic and flammable when exposed to high temperatures,” says Coleman. “Many believe they can get away with heating these containers for only a few seconds, but this is not the case.” If you bring leftovers home in a styrofoam box or want to reheat coffee in a styrofoam cup, transfer it to a microwave-safe plate or glass first.
2. Kitchen sponges
Though heating methods, such as microwaving or boiling, reduce bacteria on sponges by 60 percent in laboratory tests, this only happens the first time the sponge is cleaned, says Candess Zona-Mendola, editor of MakeFoodSafe.com. “The remaining 40 percent of bacteria that survived cleaning methods recolonize at a faster rate, effectively repopulating the sponge.” Gross! Just get a new sponge—here are some of the best sponges you can buy.
3. Travel mugs
“Many travel mugs are made from stainless steel,” says Doug Rogers, president of Mr. Appliance, a Neighborly Company. “When put in the microwave, stainless steel blocks the heat from warming liquid and can damage your microwave.” The exception? If your travel mug is fully plastic, it may be good to go. Get a quality travel mug, and be sure to check the bottom of the label to ensure its marked as microwave-safe.
Here’s one you probably never thought of before: “Not that many people decide to microwave their grapes, but these small berries can catch fire or explode within a microwave oven,” says Coleman. Why? Grapes and raisins emit plasma when microwaved, says Rogers, which can cause them to smoke and even explode.
5. Anything with metal trim
Any plates or bowls that have a metallic trim—think Chinese takeout containers—should never go in the microwave. “Not only can they be a fire hazard, they can short-circuit the microwave itself and ruin the functionality of the device,” says Coleman. For this same reason, any and all metal (utensils, cookware, containers, aluminum foil, etc.) should also stay out of the microwave.
6. Plastic storage containers
“Some plastic containers may contain BPA, which can release toxic fumes and leach into your food when heated,” says Rogers. “If you choose to use them in the microwave, double check to make sure your plastic storage containers are labeled microwave-safe.” Luckily, our top-rated food storage containers are all microwave-safe.
Though Pinterest hacks may lead you to believe otherwise, hard-boiling eggs in the microwave is not a good idea. “If you cook an egg in shell in the microwave, it’s likely to explode,” according to The Incredible Egg. “Microwaves heat so quickly that steam builds up faster than an egg can ‘exhale’ it through its pores and the steam bursts through the shell.” If you’re microwaving a cracked egg, be sure prick the unbeaten yolk with the tip of a knife to allow steam to escape. In that case, you can absolutely make a breakfast casserole or an omelet in the microwave, no problem.
8. Repurposed food containers
According to the USDA, single-use containers like butter tubs and yogurt containers should never be microwaved. These containers can warp or melt, which could cause harmful chemicals to leach into the food. If you save those old yogurt containers and other single-use food containers, just be sure you don't microwave them.
9. Breast milk and formula
According to the FDA, breast milk or infant formula should not be heated in the microwave. Microwaves heat milk and food unevenly, resulting in "hot spots" that can scald a baby's mouth and throat. There’s also some evidence that these high temperatures can diminish the quality of human milk. Instead, invest in an award-winning baby bottle warmer to keep your baby safe.
Huh?! Hear us out: “We’ve all experienced that moment where you’re trying to use the microwave timer for cooking, but accidentally turn on the “cook time” feature, engaging the appliance’s heating action,” says Rogers. But beware of turning on the microwave with nothing in it! “Since there’s nothing to absorb the microwaves (i.e. food) the waves have nowhere to go, and are then absorbed by the actual appliance, which could cause it to combust if left running for an extended time period.”