Think Twice Before Putting These Common Things In The Microwave

In 1945, one Percy Spencer, a brilliant self-taught engineer, received a patent for a groundbreaking invention of his: the microwave oven. Cooking hasn't been the same since this uber-convenient appliance hit the market. Yet despite its popularity and presence in the homes of millions, not everyone has the record straight about what should and shouldn't go in the microwave. You might know the most obvious no-nos, including the errant fork or crumpled tin foil, but some other hazards might shock you (literally).

Even after 80 years of technological advancements, manufacturers haven't figured out how to make some innocuous-looking things microwave-safe. In this list, you'll learn about the top 13 items you should keep away from the interior of your microwave oven. Some of them are head-scratchers, others are obvious upon a second thought, but all have the capacity to damage you, your microwave, or your whole home. Take heed in order to keep sparks, smoke, and even flames out of your kitchen.

If you were allowed to microwave your own food as a kid, you probably got a stern warning from the adults in your life: Metal utensils never belong in there. But did you know that metal can sneak in through less obvious ways? Think about the thin wire handle on a Chinese takeout box, a mug or thermos with a steel coating, and even dishes with metallic paint or decorations. You absolutely need to search your items for metal before nuking them, or you might have a fire on your hands.

The radioactive waves that give the microwave its name heat your food as they bounce around inside the appliance. These microwaves have electrons in them, which interact with the water molecules in your food. When steam is released from your meal, these electrons are also discharged. However, when metal is introduced to the mix (especially bent or crinkled metal like tin foil), electrons can go haywire. 

Unlike water, which releases the bouncing electrons via steam, metal doesn't have that quality. The electrons start to cluster in one spot, then violently release their energy via fire and mini-electrical storms. The bottom line: Don't microwave anything that might contain even a little bit of metal.

Anyone who's ever tried to reheat bread in the microwave knows that it winds up less soft and warm and more like a rubbery blob or leaden brick. This transformation from a crusty, delicious slice to a hockey puck happens because the heat from the microwave changes the bread's sugar molecules. Once the sugar molecules in bread heat up to 212 degrees Fahrenheit or higher, they melt, turning them from soft and well-integrated into a crystallized mess. 

These sugar crystals will then harden, which is why your bread feels very chewy and almost rubbery when it comes out of the microwave, then turns rock hard in a matter of minutes. The same thing happens to muffins, donuts, and other bread-adjacent items. The best way to reheat a loaf of bread or other baked treat is to bypass the microwave and pop it into the oven instead. Just wrap it in a blanket of foil and warm it in a pre-heated oven. 

If you don't want to try the oven, you can opt for a skillet; just be sure to flip bread slices frequently, and know that heating up muffins or other goods will trickier. And of course, a toaster is best if you want to breathe new life into just one or two slices of bread.

You wouldn't slice up a plastic container and eat it with a knife and fork, would you? Yet when you heat up certain plastics in the microwave, you'll basically be eating them, once you consume the food or drink they're touching. Some plastics constantly release microscopic particles into materials they're in contact with, and heating them up in the microwave speeds up this release process. 

This isn't to say you can never microwave plastic — doing it cautiously starts with identifying microwave-safe containers. One-time use plastic containers, like water bottles, takeout trays, or margarine tubs, are among the most volatile plastics that tend to release micro-particles into your food. Instead, only heat up microwave-safe plastic containers. You can examine the container itself to find a symbol or instruction that says if you can microwave it or not. When in doubt, just don't do it.

Ideally, you would heat your food in glass containers instead. However, not all glass is microwave-safe, either, and the wrong kind can easily shatter. To prevent this, look for the microwave-safe label on your glass bowls, too. Usually, manufacturers place this symbol on the bottom of a bowl or glass.

Who'da thunk that few carrot sticks could turn into Fourth of July sparklers in the microwave? If you try nuking this veggie, you might see an alarming series of flashes inside the oven. This is because carrots contain metallic minerals, such as magnesium, iron, copper, and selenium. Kale, sliced grapes, bell peppers, spinach, and even hot dogs count among the foods that can light up your microwave like an Independence Day fireworks show. In the case of hot dogs, salts and additives in the meat might be spark-inducing.

This strange phenomenon is called arcing, and it doesn't always happen. You might microwave some mixed veggies and have it turn out fine, only for the next time to result in a fire or the electricity in your kitchen flickering on and off. Factors like watery (i.e. flame-retardant) ingredients on top of your food and the environment in the microwave can discourage arcing, so if you nuke a creamy carrot casserole instead of plain carrots, it'll probably be okay. But you'd probably prefer to avoid sparks, fires, and power outages altogether. If you do decide to risk it and heat these veggies in the microwave, watch for sparks and stop the oven immediately if you notice any.

If you like to stash your leftovers in a resealable plastic baggie, you've probably at least contemplated reheating them in the same bag to save time and dirty dishes. While some zip-top bags are labeled as safe for the microwave, this can vary from brand to brand, and even product to product. It's the same deal as single-use plastics and Styrofoam: Potentially harmful substances can leach into your food as the bag heats up. Always check your box or package of plastic bags to see if you can microwave them, and even if the manufacturer says it's safe to do so, you need to take several precautions.

First, place the bag on a microwave-safe dish or plate. Then, create a steam vent in the bag by opening the top by about one inch. Finally, as you microwave it, watch the bag for signs of melting. Although the plastic in microwave-safe bags shouldn't leach chemicals, it will still melt if the food inside it gets too hot. Even if no melting occurs, you could get burned if you touch the hot bag, so open the microwave and let it rest until it's cool enough to grab. Honestly, it might be easier to just dump your leftovers out of the bag and heat them in a dish, instead.

To keep your microwave from wearing out too soon, or even catching fire, you should only run it when food or liquid is inside. Leftover mac and cheese or a cup of slightly tepid coffee can soak up the large number of microwaves that bounce around the oven's interior. In contrast, when these microwaves have nowhere to go, they essentially start cooking the inside of the appliance instead. 

If you heat up an empty microwave, your unit may stop working — or it may start blazing. If you've accidentally run the microwave with nothing in it for more than a scant few seconds, you need to test the unit to make sure it's still safe to use. Microwave something simple like a mug of water. If the oven runs fine, with no erratic behavior or sparks, it should be okay to use. If it doesn't operate or works improperly, you may have damaged it. 

You can likely get your microwave repaired and continue to use it, but it's best not to have to explore that possibility. Always keep food or liquid in the microwave while it's running, whether you're reheating tea or using lemon water to clean the inside.