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Mug of water -

Water that is heated in a microwave can quickly become superheated. While you might not see any bubbles form, they can quickly appear when you add a tea bag, spoon, or even just move the water. In rare cases, it might even explode.

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Mushrooms -

Since mushrooms are sensitive to high heat, microwaving them can cause changes to their texture and flavor. Furthermore, reheated mushrooms are extremely vulnerable to bacteria and other microorganisms, which can give you a stomach ache. It's best to reheat them gently on the stove top or in the oven.

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Leafy greens -

When heated in the microwave, leafy, green vegetables like spinach or kale run the risk of converting naturally occurring nitrates into nitrosamines, which can be harmful in large quantities. Some nitrosamines are carcinogenic and can affect the body's ability to carry oxygen.

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Beets -

Just like spinach, reheating nitrate-rich beets and turnips can convert them into nitrosamines. Good thing they're just as delicious cold.

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Processed meat -

Bacon, hot dogs, lunch meat, and sausages often contain chemicals and preservatives that extend their shelf lives. Unfortunately, microwaving them can make those substances worse for your health. Sautéing may be the safest option when it comes to reheating processed meat. 

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Tomato sauce -

Heating tomato sauces in the microwave often ends in splatters. The heat and steam produced by the sauce when warmed has a difficult time escaping through the thick sauce. 

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Tomato sauce -

The steam builds up until it bursts onto the microwave walls. In some cases, the sauce can even explode when you stir it, which could lead to burns and stained clothes. Instead, reheat any sauces in a small pan on the stove. 

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Chili peppers -

When it comes to chili peppers, whether fresh, roasted, or incorporated into dishes, reheating them in the microwave can be risky. The capsaicin, which makes them spicy, can vaporize or break down under high heat, causing the peppers to heat unevenly and release more of this substance into the dish. Instead, gently warm up spicy dishes on a stove top to ensure even heating and better texture. 

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Frozen fruit -

When frozen fruits are exposed to the microwave, the rich amount of glucosides present are converted into carcinogenic substances. 

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Potatoes -

Don't worry, you can still speed-cook your raw spuds in the microwave. The danger comes when you try reheating cooked potatoes. Potatoes often house Clostridium botulinum, the botulism bacteria. When they're cooked and not immediately stored in the fridge, spores of the bacteria can multiply. And microwaving the potatoes won't kill the bacteria either. Be sure to move cooked potatoes that won't be eaten into the fridge as quickly as possible, and reheat in the oven. 

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Grapes -

Don't top your oatmeal with a handful of grapes and slide the whole dish in the microwave. Grapes become superheated, and the sugary pulp quickly turns into molten plasma, which could explode in the microwave. 

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Eggs -

Reheating eggs in the microwave can leave them tasting rubbery and tough. If you have leftover scrambled or fried eggs that you'd like to warm up, do it gently on the stovetop over low heat, stirring or flipping frequently to evenly distribute the heat. 

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Hard-boiled eggs -

When it comes to hard-boiled eggs, it's best to eat them cold or reheat them in a bowl of warm water rather than trying to microwave them. Whether in the shell or peeled, hard-boiled eggs heated in the microwave release steam. The steam can't escape the whites, so pressure builds. Then, when you cut (or worse, bite) into the egg, the steam is released instantly. The resulting explosion may burn you. 

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Steak -

Microwaving steak can leave it dry and overcooked, robbing the meat of its juicy texture. Instead, reheat it in the oven for about 20 minutes, or on low heat on the stovetop. 

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Chicken -

Chicken, especially the breast, tends to become tough, dry, and chewy when reheated in the microwave. Instead, just like steak, reheat it slowly in the oven or on the stovetop.

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Nachos -

Throwing your nachos in the microwave can make the chips soft and the cheese rubbery. Instead, opt to reheat your nachos in the oven at a low temperature. This will help maintain the crispness of the chips and ensure the cheese melts evenly. 

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Pasta -

Pasta often heats unevenly in the microwave, resulting in spots that are too hot and others that are too cold. Instead, try reheating it in a skillet on the stove top and add a bit of sauce or water to rehydrate the pasta.

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French fries -

French fries become disappointingly soggy and gross when reheated in the microwave. 

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Anything fried -

The same applies to other fried foods. Therefore, the best way to reheat them is in an oven, or even better, an air fryer to help retain that crispy texture. 

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Pizza -

When reheated in the microwave, pizza can turn soggy, with the crust losing its original crispness. If you don't enjoy cold pizza, try reheating it in the oven on low heat for at least 15 minutes. This will heat your pizza evenly while preserving the crust's texture.

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Breast milk -

Microwaving breast milk is generally discouraged due to the risk of uneven heating, which can create hot patches that could burn an infant's mouth. Moreover, the harsh process can increase the risk of chemical leaching from plastic containers, or cause changes in the milk's nutrients, enzymes, and antibodies. 

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Breast milk -

Instead, reheat breast milk using a bowl of warm water or running it under warm tap water for a few minutes. Remember to always test the temperature before feeding. 

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Rice -

Microwaving rice can turn its fluffy texture hard. Instead, try steaming rice in a pot over the stovetop. Add a small amount of water, cover the pot, and let it steam slowly for about five to 10 minutes to rehydrate your grains. 

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Bread -

Microwaving most types of bread will turn it tough and dry. Instead, try wrapping your bread in foil and warming it in the oven on low heat. 

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Fish -

As with steak and scrambled eggs, fish is a delicate protein prone to overcooking. Have you ever tried eating overcooked fish? You might as well chew on rubber bands.

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Seafood -

The same goes for seafood, which can dry out quickly and leave an unpleasant smell. Instead, warm it up gently in the oven or on the stovetop to help it maintain its tender texture and minimize odors.

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Pastries -

When you reheat pastries in the microwave, they can quickly lose their crispiness and become soggy or stale. To preserve the crunch, heat them up in the oven on low heat for about 10 minutes. 

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Coffee -

Reheating your coffee will only break down any of the aroma and flavor that it once had, leaving it bland and stale. Your best option for reheating coffee would be to put it in a pot on the stove. 

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Foods that have already been reheated -

Never reheat leftovers more than once. This is because each time you reheat and refrigerate food, you're introducing the possibility of bacterial contamination, especially if the food takes too long to heat up or cool down.

Sources: (Tasting Table) (Southern Living) (Real Simple) (The Healthy) 

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