Last updated on May 30th, 2024
Ever heard that one about microwaving water being bad for plants—and by extension proving microwaves are bad for our health? It’s a favourite example used by those peddling pseudoscientific claims regarding microwaves. There are some real harmful effects of microwave cooking, but most are malarky, and so is this one. The story goes something like this: water is microwaved and used to water a plant. The plant then grows poorly or dies when compared to a plant sitting next to it, which has been watered with boiled water. If you’re up for it, try this experiment at home. Water two plants over time, one with microwaved water and one with water boiled on a stove (both cooled down to room temperature, of course). Everything else—the amount of water, sunlight, and type of plant—should be the same. What you’ll find is no difference in the growth or health of the plants, debunking the idea that microwaved water is in some way poisoned. And when you do find this, please realise that whoever told you this isn’t really very credible and you should really question any other claims they’re making. We will set those myths straight, but first let’s cover how microwaves can actually be bad for your health.
The Real Danger of Microwave Ovens
Uneven Cooking and Food Poisoning
Perhaps the most significant risk associated with using microwave ovens is uneven cooking. Microwaves aren’t powerful enough to penetrate deeply into denser foods. As a result, only the outer layers are heated directly by the microwaves, with the inner warmth being achieved slowly through conduction. This can lead to cold spots in the food, particularly in the centre, where bacteria like Salmonella and E. coli can survive if the food isn’t heated through. This is a particular concern with dense, high-protein foods like poultry, eggs, and certain meats, where ensuring thorough cooking is vital in preventing food poisoning.
The danger of uneven heating extends to heating liquids, such as baby formula. The risk of scalding is particularly high with infants, as hot spots in the liquid can cause burns if the formula is not mixed well and tested before feeding. This potential for direct physical harm underlines why health professionals recommend against using microwaves for heating baby bottles or formula. The consequences of getting it wrong, especially with tired or distracted parents, can be lethal.
To combat uneven heating, a simple practice is to pause the microwave halfway through the cooking time to stir the food, rotate the dish, or even rearrange the items within the microwave. Additionally, allowing the food to stand for a few minutes after microwaving helps the heat distribute more evenly, as it naturally flows from hotter areas to cooler ones. This practice helps to ensures safer food consumption while also enhancing the food’s overall texture and taste.
Is a Microwave Dangerous when used for Heating Plastics?
Microwaving plastics is a cause for real concern – if not overblown. Heating food in some or even all plastics can be risky. The risks associated with using certain plastics in the microwave mainly revolves around chemicals potentially leached into food, such as BPA (Bisphenol A), styrenes and phthalates.
BPA (Bisphenol A), styrenes and phthalates are chemicals found in some plastics, like polycarbonate and PVC, which can leach into food when heated. These substances are known endocrine disruptors and carcinogens, mimicking or interfering with the body’s hormones. While typically the amount of these chemicals leaching from plastics is very small – often in quantities considered safe by regulatory bodies – the long-term effects of continuous exposure are still under scrutiny.
Fortunately, the likelihood of encountering harmful plastics like PVC or polycarbonate in microwave use is low – with the exception of polystyrene takeaway containers and commercially common PVC cling film. Most microwave safe containers – even single use takeaway containers – are made from polypropylene (PP), labelled with a resin code #5. This type of plastic is the only inherently microwave safe plastic, is unlikely to contain BPA or phthalates, and is chosen for its heat stability and safety properties. While polypropylene is generally microwave safe, the best practice is to use containers that are explicitly labelled as microwave safe. This label is a manufacturers assurance that the product can withstand microwave heat without degrading and that it does not contain or release harmful chemicals. This is especially important if you wish to ensure against any potential, albeit unlikely, contamination from BPA or phthalates. As well as polypropylene containers most meat is packaged in PET with a resin code of #1 which is not microwave safe, and clingfilm is usually low density polyethylene – resin code # which is closer to microwave resistant than microwave safe. Regardless, these plastics are extremely unlikely to contain phthalates or BPA, though are more likely to melt. Check out our full guide How to Know if Plastic is Microwave Safe for a more detailed guide.
A growing, and valid concern is the potential shedding of microplastics from plastic containers when microwaved, particularly from older or degraded containers. The health implications of ingesting microplastics are still being studied – they may carry toxins and accumulate in the body over time. If the potential risks associated with plastics are a concern for you, consider investing in microwave safe glass containers. Glass is very inert and poses no risks of chemical leaching or microplastic shedding. Glass can provide peace of mind to those seeking the safest microwaving option.
The Made Up Reasons a Microwave is Bad for Health
Microwave Radiation Risks
One enduring myth is that microwaves produce radiation that makes food radioactive, and which can and often does leak out of the microwave irradiating anyone nearby as well. Microwaves don’t change the chemical structure of food to make it radioactive. Microwaves use non-ionizing radiation, which does not have enough energy to change the chemical structure of food components or make them radioactive. This type of radiation is similar to radio waves or the light waves from your table lamp, and is far removed from ionizing radiation (such as X-rays and gamma rays). To make something radioactive, the radiation it is bathed in must be powerful enough to knock particles out of its atoms. Non-ionizing radiation, like visible light, infrared, and microwaves, does not have enough energy to remove tightly bound electrons from atoms or molecules and cannot make materials radioactive.
It’s true, microwave radiation can be dangerous. After all, the very principle of a microwave oven is to use this radiation to heat food quickly and efficiently. The concern though is not about radioactivity, but about a microwave ovens potential to cause burns in the same way as a direct flame can. On face value, concerns about this radiation leaking might seem reasonable. An analogy illustrates why it is not: a fire in a fireplace provides warmth and comfort, but sticking your head into it is likely to be lethal. Similarly, while a microwave oven is generally safe when used correctly, improper use—like tampering with its safety mechanisms—can be hazardous. The risk microwave radiation does pose is not a concern of radioactivity, rather in their ability to burn the same way a fire might. A stove poses a greater hazard.
Microwave are safe in that they are engineered with multiple safety features to prevent improper use, as well as to prevent significant radiation leakage. The small amount that might escape, which can sometimes interfere with Wi-Fi signals (which also uses microwave radiation) – while annoying – is harmless. Regulations ensure that the level of microwave leakage is far below that which could cause harm to humans. With over 50 years of widespread use and a strong safety record, it’s safe to say that microwaves are safe, when used as intended.
Does Microwave Cooking Kill Nutrients?
Yes – microwave cooking will remove nutrients from food. However, microwave cooking preserves nutrients better than most other conventional cooking methods. Water soluble vitamins like vitamin C and some B vitamins are particularly vulnerable to high heat and long cooking times. Since microwaving usually requires less time and heats the food up for a shorter period, it can help retain these heat sensitive nutrients more effectively. Microwaving broccoli, preserves its vitamin C and antioxidant content more than steaming or boiling for example. Boiling vegetables on the stovetop will cause some of their nutrients to leach into the cooking water, which is usually discarded. Microwaving vegetables usually uses less water and reduces this nutrient loss. Furthermore, the quicker cooking time in a microwave can help preserve antioxidants and vitamins that degrade or oxidise over prolonged exposure to heat
While all cooking can diminish some nutrients, it transforms food in several beneficial ways. It enhances digestibility, improves the availability of certain nutrients, eliminates harmful microorganisms, and reduces compounds that inhibit nutrient absorption. Consequently, despite the varying effects of different cooking methods on nutrient levels, the overall benefits of cooking, including microwave use, significantly enhance our diet by making food safer, more digestible, and generally more nutritious.
Microwaves Will Poison you
This pervasive myth largely stems from two widely discredited “studies” that have fueled misconceptions about microwave cooking.
The 1989 Lancet study: Aminoacid Isomerisation and Microwave Exposure
Actually, just a letter to the editor, and not a study. The author, Lubec, microwaved baby formula for 10 minutes and found that some amino acids in the formula had been converted to cis-3 hydroxyproline, cis-4 hydroxyproline, and D-proline amino acids which were thought to be possibly toxic at the time. Lubec failed to disclose crucial experimental details like microwave power and the temperature reached. He later admitted that the formula had been placed in a pressure vessel and heated to an extreme 175°C. Moreover, it’s since been proven cis-3 hydroxyproline, and cis-4 hydroxyproline are both a part of normal metabolic processes in humans, particularly in the synthesis and maintenance of collagen, and that D-proline isn’t toxic either and is found abundantly in commercial dairy products. Good work Lubec – If you seal formula in a pressure vessel and microwave it for 10 minutes to 175°C, it will convert some amino acids to slightly different ones that carry no danger.
The 1990 Franz Weber Study
This tabloid style report authored by Hertel and Blanc in Journal Franz Weber (Issue 19), lacked peer review and is a publication far from the scientific mainstream. It involved only eight volunteers consuming microwaved food and aimed to assess various blood markers. Not only was the sample size too small to draw any significant conclusions, but the claims made were also alarmingly sensational stating that “… microwave ovens are more harmful than the Dachau gas chambers…” and “… it is certain that you will die from cancer”. The data showed that all blood analysis results fell within normal variation ranges. One of the authors of the paper (Blanc) later stated “I totally dissociate myself from the … experiment carried out in 1989, which was published without my consent by the co-author of the study… The results obtained do not in any circumstances justify drawing any conclusions as to the harmful effects of food treated with microwaves”.
Actually, it Turns out Baking, Frying, Roasting, and Grilling Might Poison you
While the harmful effects of microwave cooking are entirely discredited, some foods when cooked at high temperatures, such as those in baking, frying, roasting, and grilling, can produce suspected and known carcinogens: acrylamide, heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs).
Acylamide is most likely to form when starchy foods like potatoes or bread, are cooked at high temperatures through baking, frying, roasting, or grilling until browned or burnt. You don’t find acrylamide in uncooked, boiled, or microwaved food. Acrylamide is recognised by health authorities including the World Health Organization and the International Agency for Research on Cancer as a potential human carcinogen. This concern is based on studies conducted in laboratory animals, showing that high levels of acrylamide can cause cancer in these animals. However, it’s important to note that the levels of acrylamide in food are much lower than those used in these studies, and the direct link to cancer in humans is still not conclusively proven. To minimise acrylamide formation, cook food until it goes yellow, not brown or black, though if you cook at too low a temperature you are less likely to kill off bacteria, so there is more risk of food poisoning.
Besides acrylamide, cooking meats at high temperatures can lead to the formation of heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), which are chemicals found to increase cancer risk in animals and potentially in humans. HCAs are formed when meats like beef, poultry, and fish are cooked at high temperatures, especially during methods that involve direct contact with an open flame or a hot metal surface, such as grilling or pan-frying. These compounds develop as a reaction between amino acids and creatine within the muscle meats under intense heat. PAHs are produced when fat and juices from the meat drip onto the heat source, creating smoke. This smoke envelops the meat and deposits PAHs onto its surface.
Both HCAs and PAHs have been identified as potentially carcinogenic to humans. Studies in rats have shown that exposure to these compounds can cause various types of cancers, including stomach, colon, and breast cancer. While translating these results directly to human risk is complex, there is enough evidence to suggest a potential increase in cancer risk associated with consistent consumption of meats cooked by high-temperature methods.
Microwave cooking, in contrast typically does not reach the temperatures necessary to produce acrylamide HCAs and PAHs. Not only does microwaving help in retaining more nutrients by reducing cooking time, but it also avoids the formation of harmful chemicals that are associated with other cooking methods. While each cooking method has its pros and cons, microwave cooking stands out for both its efficiency in nutrient retention and its lower risk of generating food-related carcinogens, making it a sound choice for health-conscious individuals.