When using a microwave to heat baby milk was banned in the USA, it sent a clear message: this device is potentially dangerous. It was quickly explained that the ban was intended to avoid the risk of toddlers being burned, because the heated fluid has a much higher temperature than the container that it is in, and the carer’s carefulness often leaves much to be desired. But the fear of microwaves nevertheless remained.
Microwaves had been banned from use in the USSR (1976, which was repealed only after the change of regime) due to the risk of cancer. Perhaps they are harmful but we do not know for sure as there are no official scientific studies to confirm their harmfulness. Most people use microwaves with no apparent ill health effects but there are others who believe that microwave radiation might be harmful.
Nowadays, many people, especially those who are leading a ‘fast’ lifestyle, cannot imagine reheating meals any other way than by using the microwave. Probably more or less the same number of people claim that dishes prepared in this way are unsavoury and unhealthy and that microwaves themselves are a source of harmful radiation. We will not be writing about the taste of dishes, because that is a matter of preference, but will instead focus on how microwaves work and how they heat dishes.
As the name of the device suggests, microwaves heat meals using electromagnetic radiation with a wavelength of about 12 cm. The radiation is absorbed by the water molecules in each dish. They start to oscillate (rotational oscillation) absorbing the energy of the absorbed microwaves. However, these vibrations are strongly suppressed by other substances (chemicals) surrounding the water molecules contained in the meal that is being heated.
As a result of this mechanical interaction (resembling the behaviour of a mixer in a dough bowl), the previously absorbed energy is transferred back to the meal, with which the microwave radiation does not interact directly, causing it to heat up. Also, the warming of the container is a secondary effect, as microwave containers do not absorb radiation of such frequencies.
Microwave radiation creates a standing wave inside the oven, magnetron waves emanate from the opposite side of the oven. This means that some places in the dish will be heated significantly (where the arrows of the standing wave, i.e. the peak of the wave, are), while others in the places of wave nodes (with zero amplitude intensity) will remain cold. To avoid such uneven heating of dishes, they are placed on rotating stands or an additional rotating reflector is used and changes the distribution of intensity within the oven.
The phenomenon of microwave interactions with food (water) was accidentally discovered by the American Percy Spencer while he was working on the construction of radar equipment. When experimenting with a magnetron, which is the source of microwaves also in the home appliance, he felt that the chocolate bar in his trousers started melting. On the other hand, an egg exposed to microwaves exploded. These troublesome events made it possible for him to launch the first microwave oven in 1947. Its dimensions differed significantly from today’s models, as its weighed in at 338 kg and was 1.65 m high. The first devices were water-cooled which meant that their use was restricted to bars and restaurants only.
There are a lot of opinions about the harmfulness of food that is prepared using microwave ovens as well as their negative impact on people nearby. However, research has shown that no chemical changes (changes in molecular structure) occurred as a result of the microwaves passing through the food. Also, microwaves do not have a significant impact on the health and well-being of their users. A microwave oven forms a so-called Faraday’s cage whose metal construction blocks all electromagnetic waves from flowing outside of the device.
The properties of the cage are not negated even if a glass (plastic) door is used through which we can observe the dishes inside. This is because the door is covered with a metal mesh that is considerably smaller than the microwave wavelength, which prevents the waves from being emitted outside of the oven. On the other hand, opening the door automatically turns the device off. It is interesting that the Soviet Union introduced a ban on the use of microwave ovens in 1976, due to the risk of cancer that was discovered by Soviet scientists. This was also partly due to much stricter standards than those that had been adopted in Western Europe.
Before using a microwave oven for the first time, it is advisable to read the operating instructions and safe handling rules carefully, focusing on the information concerning the containers that may be used and directions on how to cook or defrost food.
Some people say that if the reports of the harmfulness of microwaves were true, then the considerable evidence would support that claim. They say that the black PR of the microwave stems from mindless repetition of claims that were not fully tested. Microwaves are electromagnetic waves — much the same as radio waves, light, infrared, ultraviolet and X-rays. But unlike the last two, microwaves do not damage the structure of chemical compounds. Isolated portions of the electromagnetic wave (called photons), in the case of microwaves, are unable to change the structure of any molecule in a living organism because they carry too little energy.
Yes, if you expose your body to an enormous stream of photons that correspond to a high-intensity wave, you can expect a significant increase in the temperature of your body. For example, the proteins may break down but exactly the same factor, high temperature, leads to their congealing in the pan! Microwaves are just as dangerous as the light emitted from a bulb. If we touch it, we will be burned, but we are safe when we keep our distance. So, if the microwave is not damaged, then it will not emit hazardous microwaves. And the probability of a breakdown of a microwave oven is no different than that of, for example, washing machines breaking down and receiving electric shocks during washing.
Some research suggests that electromagnetic radiation (every microwave has a radioactive source comparable to an airborne radar) has a carcinogenic effect (can cause cancer) and is mutagenic, it changes the DNA structure of humans. In theory, radiation is emitted only on the inside of the device. In practice, however, oven doors often leak. Therefore, the people waiting for dinner to warm up or operating the device all day, are at a higher risk of exposure.
The biological effects caused by microwave radiation can be serious, although not specific, so we often do not connect them with the cause. These might include chronic fatigue, somnolence, trouble with concentration and memory, frequent headaches, also dysregulation of the hormonal and nervous system resulting in emotional instability and fertility problems.
Changes in the body under the influence of radiation also results in a decrease in immunity and therefore increases the risk of infection and development of cancer cells. If you have to use microwaves, try not to stand close while they are on! Of course, every product that is rolled out on the market must meet the standards that limit how much radiation they can emit.
Devices are tested before they leave the factory but during frequent use, the door’s electromagnetic seal will inevitably wear out and waves could at that point, be emitted from the device. Microwave radiation is not visible, there is no clear signal that something is not functioning properly. If there is a dishwasher or washing machine, we have telltale signs of malfunction, e.g. water on the floor, whereas in the case of microwave ovens malfunctions usually remain unnoticed.
Food Matters (2013) Are You Still Using A Microwave Oven? [Online] http://www.foodmatters.com/article/are-you-still-using-a-microwave-oven(Accessed 26/06/2017)
World Health Organization (WHO) (2005) Electromagnetic fields & public health: Microwave ovens [Online] http://www.who.int/peh-emf/publications/facts/info_microwaves/en/ (Accessed 26/06/2017)
Apparently Apparel (2011) Why Did Russia Ban The Use of Microwave Ovens? [Online] http://www.apparentlyapparel.com/news/why-did-russia-ban-the-use-of-microwave-ovens (Accessed 26/06/2017)
Spector, D. (2014) How do microwaves work [Online] http://www.businessinsider.com/how-do-microwaves-work-2014-6?IR=T(Accessed 26/06/2017)
Food Safety and Inspection Service, United States Department of Agriculture (2006) Microwave Ovens and Food Safety [Online] https://web.archive.org/web/20110108064919/http://www.fsis.usda.gov/PDF/Microwave_Ovens_and_Food_Safety.pdf (Accessed 26/06/2017)
http://www.arpansa.gov.au/RadiationProtection/Factsheets/is_Microwave.cfm#6 (Accessed 26/06/2017)
IARC (2011) WHO: IARC classifies radiofrequency electromagnetic fields as possibly carcinogenic to humans [Online] http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf (Accessed 26/06/2017)