15 Things Never to Put in the Microwave

If you don’t know it by now, we’re here to tell you: Putting metal in a microwave is a huge no-no! Many microwaves are lined with metal, which acts like a mirror, bouncing microwaves around the box until they’re absorbed by the food. That’s great for heating food, but metal, unlike your leftovers, is a great conductor of electricity; it reflects heat rather than absorbing it, and that’s a big problem in a microwave. At best, a little metal in the microwave prevents food from cooking properly. At worst, the resulting heat will create sparks that could cause a fire and render your microwave unusable. 

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Fine china has no place in the microwave, especially if it is trimmed with metal accents like platinum or gold bands. Don’t forget: That lovely metallic trim is just that—metal. And when metal is microwaved it can result in sparks, fire, and ruined dinnerware. Before you pop cups and plates in the microwave, look for a message on the bottom of each dish stating that it’s microwave-safe. If your dish is not clearly marked as such, set it aside and reach for a glass or ceramic container that can take the heat.

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A cold kitchen cupboard can cause honey to crystallize, which is cool if you’re conducting a science experiment, but a drag if you want to use the squeezable sweetener. While a short zap in the microwave can return crystallized honey to its liquid state, don’t try this with the honey still in the squeeze bottle! Most condiment containers, including squeeze bottles for honey, hot fudge, and mustard, are not microwave-safe. The soft plastic from which the bottles are made may melt, explode, or catch fire. If you want to microwave crystallized honey, scoop a little out into a microwave-safe container first. If you’d rather heat the entire bottle, dunk it in boiling water for a few seconds at a time until the honey liquefies.

Busy new moms and working mothers have taken to freezing breast milk and thawing it as needed. The practice is perfectly safe, provided it’s done correctly (check with your doctor for guidelines). Microwaving frozen breast milk, on the other hand, is not a good idea. Microwaves heat milk unevenly, which creates “hot spots” in the milk that can scald the baby. Not only that, but some research has found that microwaving breast milk destroys immune-boosting proteins. The FDA suggests heating breast milk or formula under hot running tap water or in a pan of hot water that’s been removed from the stove burner. Before feeding, shake the bottle, and test the temperature of the milk on the back of your hand to ensure that it’s not too hot for baby to drink.

It seems like there are hundreds of gadgets for sale in stores and online that promise to safely and easily cook eggs in the microwave, but you’d be wise not to waste your money. No matter which gizmo du jour you use, microwaving eggs is a fast track to a big mess. The rapid heat generated by microwaves creates steam inside the egg, which often causes it to explode. What’s worse than scrubbing egg yolk off the inside of your microwave? Having an egg explode on your plate—or even in your mouth when you bite into it. If you want a nice, warm egg, stick to the stovetop.

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Plastic containers and microwaves are not a good marriage. Certain types of plastic containers—butter tubs, yogurt cups, cream cheese tubs, and even reusable food storage containers—are designed to hold refrigerated items and can’t withstand the heat of a microwave. When heated, these containers can melt and release estrogen-like chemicals, including bisphenol A, or BPA, into your food. Transfer your food to a microwave-safe glass plate or bowl to avoid unpleasant chemical contamination.

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When your morning coffee goes cold, it can be tempting to zap it in the microwave. But if that coffee is in a Styrofoam cup, back away from the microwave. Styrofoam, a soft, light plastic, melts when exposed to the high heat and rays of a microwave. When it melts, Styrofoam releases harmful chemicals into your food—so keep Styrofoam cups, bowls, and take-out containers out of your microwave. It’s important to note that Styrofoam is particularly bad for the environment, and most curbside recycling programs won’t accept the material for pickup. So, yes, pass on putting Styrofoam in the microwave, and while you’re at it, avoid bringing it home in the first place. 

Again with the coffee! Travel mugs are typically constructed of stainless steel or plastic—two items that should never be microwaved. Stainless steel blocks microwaves from warming the liquid inside the mug and could spark or cause a fire. Plastic mugs, on the other hand, may melt or release harmful chemicals when heated. Rely on the stovetop to reheat your coffee or tea—or brew yourself a fresh beverage.

Those convenient microwave popcorn bags may have given you the impression that it’s safe to heat paper bags. Not so! Not all paper bags are created equal. Popcorn bags are constructed of a material that contains susceptors that are designed to absorb the rays from the microwave and prevent the paper from catching fire. Paper lunch bags or grocery bags do not have these susceptors, which means they can be a hazard in the microwave.

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Another item that should never go from fridge to microwave? Chinese take-out containers. The handles on these familiar white boxes are usually made of metal. Though small, these handles can cause sparks or catch fire when heated in the microwave. Transfer your leftovers to a glass plate or bowl before heating them up for a quick meal.

Hot peppers and microwaves are a recipe for pain. Like eggs, peppers can explode when heated too quickly in the microwave—and they can even catch fire. The other problem with peppers is capsaicin, the chemical that makes them hot and spicy. When microwaves hit the pepper, capsaicin turns into an aerosol, resulting in a homemade pepper spray that can burn your eyes and skin the moment you open the appliance door. If you’re cooking hot peppers, use the stovetop, oven, or broiler—and always handle with care.

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Many home cooks think thawing frozen meat in the microwave is a helpful hack to speed up dinner prep. In reality this method produces uneven results and can actually cause bacteria to grow, resulting in food-borne illnesses. The reason is that different thicknesses of the meat absorb microwaves at different rates, leaving some areas cooked while others are still frozen. The safest way to thaw meat is to defrost it in the refrigerator overnight.

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Be sure never to turn on the microwave when it is empty. Without food or liquid to absorb the rays, the working components inside the unit—including the magnetron, the main element that makes the appliance operate—will absorb the radiation. This will severely damage the unit and could cause a fire or explosion.

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Don’t pop a dish into the microwave uncovered unless you’re looking for a mess to cleanup. When you’re heating up your leftovers, soups, or sauces the food simmers, bubbles, and shifts. Put a microwavable lid over your bowl or plate to keep the food contained.

When it comes to processed meats, stick to the oven, stove, or grill. Heating processed meat items (think, bacon, hot dogs, sausages, and lunch meats) lead to the formation of cholesterol oxidation products, which have been linked to coronary heart disease and other health problems.