That leftover dinner sitting in your fridge might look harmless enough, but some foods can turn from delicious to dangerous when you zap them in the microwave. Microwaving causes uneven heating, and microwave ovens can leave “cold spots” where harmful bacteria can survive. While we’ve all grown dependent on this convenient kitchen appliance, food safety experts are increasingly warning about specific foods that should never see the inside of your microwave.
According to FoodSafety.gov, 1 in 6 Americans get sick from foodborne illness each year. The culprits often hide in foods we regularly reheat without thinking twice. Let’s explore the seven foods that food safety experts unanimously agree should stay out of your microwave, and discover why these seemingly innocent leftovers could put your health at serious risk.
Hard-Boiled Eggs
When microwaved, the moisture inside hard-boiled eggs rapidly converts to steam, building pressure with nowhere to escape. The explosion risk is real and can cause burns or eye injuries from flying hot egg pieces. Shelled or unshelled, when a hard-boiled egg is cooked in a microwave, the moisture inside creates an extreme steam buildup, like a miniature pressure cooker, to the point where the egg can explode. Even scarier, the egg may burst after it’s been heated, which means the scalding hot egg can erupt in your hand, on your plate or even in your mouth. Reheating hard-boiled eggs in the microwave can be messy and potentially dangerous. The moisture inside the egg can create steam, causing the egg to explode if not properly vented. This not only creates a mess but also poses a risk of burns. Food safety experts recommend slicing eggs before reheating them gently in a pan or under hot water instead.
Rice
According to the Food Standards Agency, microwaving rice can sometimes lead to food poisoning. The issue with rice involves the common presence of a highly resistant bacteria called Bacillus cereus. When stored improperly, rice can develop Bacillus cereus spores, which can survive the reheating process and cause food poisoning. Microwaving may not heat the rice evenly, leaving some parts at a temperature where bacteria can thrive. If your rice is left standing at room temperature, it can contain spores of bacteria that can multiply and cause food poisoning, according to the National Health Service. Microwaving it won’t kill the bacteria, so you’re best eating your bowl of rice in one sitting. This condition, often called “fried rice syndrome,” has become increasingly recognized by medical professionals. The humid environment of warm rice creates ideal breeding conditions for these dangerous spores.
Chicken
Chicken, which is at risk of salmonella contamination, could be a dangerous food to microwave. Since microwaves don’t fully or evenly cook all parts of the meat, you’re more likely to be left with surviving bacteria, such as salmonella. Food safety experts warn that microwaves may not heat chicken evenly, potentially leaving cold spots where harmful bacteria can survive. If the meat you’re reheating is high in polyunsaturated fatty acids (chicken is the classic example here), then reheating it in the microwave can make it take on the dreaded warmed-over flavor. This occurs when these fatty acids react with oxygen, generating undesirable flavor notes. Sometimes microwave-heated chicken can even taste like it’s gone bad. Beyond taste issues, the uneven heating creates dangerous cold spots where salmonella can survive and multiply. It’s OK to reheat chicken once if it has been cold, but be wary of putting it in the microwave, unless you’re certain it can cook evenly all the way through.
Breast Milk and Formula
Microwaving formula or breast milk can cause uneven heating, creating hot spots in the bottle. These very hot parts of the fluid can scald a baby’s mouth. Reheating breast milk in the microwave is not only unsafe but also poses a health risk to infants. The microwave can create uneven heat distribution, leading to hot spots that can scald a baby’s mouth and throat. Additionally, the high heat can destroy essential nutrients and antibodies in breast milk, reducing its nutritional value. The Food & Drug Administration also advises against microwaving breast milk because it destroys nutrients in the heating process. Healthcare professionals universally recommend warming breast milk by placing the bottle in a bowl of warm water or using a specialized bottle warmer. The stakes are simply too high when it comes to infant safety.
Leafy Greens
When heated in the microwave, some food safety experts suggest that leafy, green vegetables like spinach or kale may convert naturally-occurring nitrates into nitrosamines, though research on vegetables shows this is generally not a significant health concern. Green leafy vegetables like spinach are rich in nitrates and iron. If reheated these nitrates get converted into nitrites and nitrosamines, which are cancerous to health and affect body’s ability to carry and supply oxygen and since spinach contains a high amount of iron, heating and then reheating the spinach may oxidize the iron present in it. Oxidation of iron causes and generates free radicals which are notorious in causing several diseases including cancer and infertility. Cooking and reheating spinach into a watery mess can concentrate the nitrates (converted to nitrite by stomach acid) in a small portion. Consuming more than 100 milligrams of nitrites a day can increase the risk of cancer, pregnancy complications, and blue baby syndromes in infants. The European Food Information Council has specifically warned about this chemical conversion process, which transforms beneficial nitrates into potentially carcinogenic compounds.
Mushrooms
Because mushrooms are sensitive to high heat, microwaving can alter their texture and flavor. Their high water content also means they tend to release moisture too quickly in the microwave, often becoming soggy or rubbery. Mushrooms are the powerhouse of proteins and have generous amounts of other minerals and by reheating them you break these proteins further, their structure changes which put the digestive system at risk and lead to severe heart problems. Apart from that, reheating them generates several toxins which contain oxidized nitrogen and other toxins. Reheating mushrooms in the microwave won’t cause any harm, however, if the mushrooms weren’t refrigerated right after cooking then you could be at risk for food poisoning. The reason for this is because the protein structure and complex enzymes can become destroyed if they’re not refrigerated immediately. If this happens, when reheated, the mushrooms can cause an upset stomach. Nutritionists emphasize that mushrooms should be consumed immediately after cooking or stored properly in the refrigerator to prevent enzyme breakdown.
Processed Meats
Compared to other meal-prep methods for reheated foods, microwaving processed meats is far more likely to introduce COPs into your diet. Processed meats like bacon, hot dogs, pepperoni, and salami are sources of cholesterol oxidation products (COPs). When you microwave processed meats, the cholesterol in the meat oxidizes and degrades. According to an article published in the National Library of Medicine, these COPs can lead to chronic health conditions, including atherosclerosis (the hardening of the arteries, which transport blood all over your body). The microwave’s intense electromagnetic waves accelerate the oxidation process in these already heavily processed foods. Food scientists have found that the combination of preservatives and microwave heating creates a perfect storm for producing these harmful compounds. A single spore of bacteria can multiply into 1,000 bacteria in a few hours, and reheating food that’s been contaminated doesn’t kill the bacteria nor remove the harmful toxins the bacteria has released into the food.
The microwave revolutionized our kitchens, but it’s not a magic solution for every reheating need. Microwaves are notorious for cooking food unevenly, allowing harmful bacteria to survive and thrive–and leaving you at an increased risk for food poisoning. Your health is worth the extra few minutes it takes to reheat these foods properly using conventional methods. Whether it’s the stovetop, oven, or simply eating foods cold, there are safer alternatives that won’t compromise your wellbeing. What do you think about these surprising microwave dangers? Tell us in the comments which foods you’ll be reheating differently from now on.
