Foods you should never put in the microwave

Microwaves can be extremely useful appliances. They heat and reheat foods and beverages and can even cook some things if you know what you're doing. Between warming up coffee or tea that's gone cold, reheating pizza, heating up microwave dinners or leftovers at the office, and more, there's little doubt that you use the microwave more than you think. 

There are some things, however, that you should never, not ever, put in the microwave. You've likely heard about containers and wraps that can cause fires, melt, or give off harmful toxins. You may never have thought, however, about the foods that shouldn't be put in the microwave. Wait, what? As it turns out, there are a number of foods and food products — even some that you may regularly microwave — that really shouldn't ever be put in the microwave. From toxins to explosions to ineffectiveness to burns, there are many reasons why these foods really shouldn't be microwaved. Read on to find out more about what foods should stay out of the microwave — and why.

Eggs in shells

Nope, you should definitely not try to hard boil an egg by microwaving it. While it may seem like a beyond-genius life-hack, it's really kind of dangerous. According to HuffPost, the high temperatures in the microwave create steam within the egg, which, as the pressure builds, can cause the egg to, well, explode. Not great.

Chili peppers

According to The Daily Meal, the capsaicin in the peppers (which is the compound in the peppers that determines how spicy they are) vaporizes when exposed to the high temperatures inside the microwave. While the peppers won't explode or anything like that, the fumes given off should be avoided if possible.

Breast milk

Many breastfeeding mamas pump and freeze breast milk so it can be saved for when needed, thawed, and then given to the baby. You need to be careful how exactly you go about thawing and heating frozen breast milk, however. According to the Food and Drug Administration (FDA), microwaving breast milk can heat it unevenly, creating hot spots that could scald your baby's sensitive palate.

A mug of water

Heating up a mug of water for hot tea or another purpose seems like a normal use for your microwave, right? It's convenient and quicker than a kettle, especially if you don't have an electric version. According to The Daily Meal, when you heat a mug of water in the microwave, it can superheat without boiling. Then, when you go to add a tea bag or stir the liquid in the mug, it boils rapidly all at once, which can cause it to spill or explode, meaning big-time burns.

Processed meats

It might seem silly, but microwaving hot dogs is a bad idea. According to research published in the journal Food Control, microwaving processed meats (typically chock full of preservatives and the like) can lead to the formation of cholesterol oxidation products (COPs), which have previously been linked to coronary heart disease, according to a 2006 study by researchers in India. So basically, it's an easy way to make a bad food even worse. If you're going to indulge, do it on the stove top.

Leafy greens

Leafy greens are a bit dangerous in the microwave. According to reporting by NPR, kale and other vegetables can spark when microwaved, potentially destroying the appliance and singeing your dinner. In an interview with NPR, Mark Golkowski, associate professor of electrical engineering at University of Colorado, Denver, said if there's a difference in electrical properties and some air for the spark to catch, it's possible the vegetables will spark. Not great when all you're trying to do is make a healthy dinner.

Oils

Oils for cooking, like olive, grapeseed, canola, avocado, peanut, and others, aren't liquids, they're fats. It can be a difficult characterization to wrap your head around, given that they look like what you'd consider a liquid to be. According to Prevention, heating an oil like olive oil, whether for cooking or beauty products, doesn't necessarily pose the danger that microwaving some other products do, but it's just simply not an effective exercise. Because there isn't any liquid within the olive oil to heat, it likely won't get as warm as you would've liked.

Uncooked rice

Rice might seem like a strange thing to never put in the microwave, but according to the UK's Food Standards Agency, rice can house spores of potentially dangerous bacteria. Microwaving it won't be enough to kill those spores, leaving you potentially susceptible to food poisoning. No thanks!

Grapes (or other fruits)

While, sure, you may not ever even consider microwaving grapes (I mean, seriously, who wants to eat a handful of warmed grapes with boiling interiors? Though roasted grapes as part of a dish are delicious), according to Thrillist, microwaving grapes is a bad idea. While you won't end up with raisins or roasted grapes, you could instead end up with balls of fiery plasma, as noted by IFLScience. Danger.

Red pasta sauce

As you likely know, red pasta sauce tends to spit, splatter, and explode all over the place whenever it takes a turn — no matter how brief — in the microwave. In a piece for HuffPost, Jon Hotchkiss, creator of This vs That, wrote "…the [insoluble] fibrous tomato chunks only block the steam's escape temporarily — that is, until such point as the volume and strength of steam overpowers the chunks… and thus causing an 'explosion.'" If red pasta sauce — and other tomato-based sauces — had an overall viscosity more similar to water, it likely wouldn't make such a mess of your microwave when you were trying to reheat it. Instead, warm the sauce low and slow in a saucepan on the stove. The sauce will stay sauce-y rather than drying out and you'll be happy because the microwave stayed spotless.

Frozen meat

Everyone has undoubtedly realized at one time or another that they forgot to take the meat out the freezer to thaw for dinner and decided to try microwaving it instead to defrost it quickly so that you can still get dinner on the table in a relatively short period of time. According to Reader's Digest, however, safely microwaving frozen meats can get a little tricky. If the heat doesn't distribute evenly, you can end up with hot spots and still-frozen spots, and the growth of dangerous bacteria. Yikes.

Broccoli

Wait, what? In most households, broccoli takes a regular turn in the microwave, but, according to a 2003 study published in the Journal of the Science of Food and Agriculture, it really shouldn't. When compared with other popular cooking methods for broccoli, microwaving destroys far more of the good-for-you nutrients that you'd normally get from eating those tiny green trees. Opt to gently steam your broccoli before eating it to keep all of those nutrients right where they belong.

Leftover potatoes

Reheating leftovers is a great idea, but you have to be careful how you do so. According to Woman's Day, you have to be especially careful about how you reheat leftover potatoes. If you let them cool down all the way before storing them in the refrigerator and then reheating them in the microwave, it's possible that their stint at room temperature encouraged botulism to grow. Microwaves can't kill off botulism, which means if you eat those potatoes, you could make yourself very sick. Better to be safe than sorry.

Frozen fruit

It may sound strange to microwave your frozen fruit, but some people do so in order to defrost it so that it's ready for other uses. According to a 2010 study published in the journal Bioelectromagnetics, popping your frozen fruit in the microwave to defrost or otherwise prepare isn't a good idea. Beneficial properties can be converted to carcinogens, and subjecting your expensive frozen fruit to microwaves can also result in adverse immunological effects. Not good. Defrost your frozen fruit in the refrigerator overnight instead.

Leftover mushrooms

Cooked mushrooms are perhaps especially likely to make you sick if you aren't super careful about how you store them prior to reheating. Because mushrooms are easy targets for microorganisms, if you eat improperly stored and reheated cooked mushrooms, you could end up with a major stomachache, which is definitely not what you wanted. Simply prep and cook the amount you want to eat or put them in the refrigerator immediately after cooking and then stir into salads and other dishes that you'll eat chilled.

Bread

If you're feeling just a little bit hungry, there's nothing that can tempt you better than a slice of warm bread with melted butter — but heat up your bread in the microwave and you'll regret it. That perfect snack will turn into a hard, chewy challenge that not even melted butter can fix and, needless to say, you should never, ever do that to any piece of bread.

According to The Spruce, bread gets funky in the microwave because of how gluten, starch, and the sugar in bread reacts when it's first heated in the microwave and then cooled. It's actually the cooling process that causes the reaction that turns your bread hard, and that means this is one thing you want to avoid using the microwave for. Instead, wrap your bread in some foil and heat it in the oven. It'll take longer, but it's worth it.

Leftovers from Chinese takeout

It doesn't matter how much you love cooking, sometimes you just want quick and easy takeout. Order out for Chinese and you're guaranteed to get enough for a few meals, but if you're tempted to reheat those leftovers in the microwave, don't.

There's a few reasons not to go the microwave route, and we'll start with the containers. LiveScience says that the Microwave Safe symbol that's on a lot of containers is there because the FDA has tested them to make sure they meet specific guidelines — and most takeout containers haven't met those requirements. Add in the fact that some have metal handles, and you don't want to be putting those in the microwave!

Your food isn't going to come out the best when you heat it in the microwave, either. It doesn't matter if you ordered egg rolls or lo mein, it's going to get soggy and it'll be nowhere near as good as it was before. Instead, take some advice from Tasting Table and reheat these leftovers in a pan on the stove top. They won't turn to mush, and you'll be able to add a fresh dash of soy sauce that all but guarantees your Chinese is just as good as it was the first time around.

Anything that's been reheated a few times before

Food safety is the most important thing that goes on in your kitchen, and that extends to reheating your food. One thing that you definitely should never put in your microwave is anything that's been reheated a few times before. According to the FDA's Ask Karen, leftovers can stay in the fridge for up to four days, but every time you reheat and cool that food, you're taking a step down in quality. Reheat it a few times or let it sit in the fridge for a few days, and it's better just to get rid of it.

The BBC also took on the question of just how old is too old to be reheated in your microwave. While their expert says that it's usually fine to microwave leftovers a few times, they also say the UK's Food Standards Agency says you should only microwave something once, and that you need to be especially careful of microwaving things like cream- and milk-based sauces, cooked meats, lasagna, and casseroles. As a general rule, trust your instincts. If you have your doubts about whether or not you should be microwaving something, you probably shouldn't be microwaving it!