Why is a microwave safe

Some people raise concerns about microwaves safety to human health. Mostly, these are really just odd concerns about the lack of knowledge about how a microwave oven works. Although microwave ovens are still in the sights of researchers and engineers, their principle is relatively simple. So why is a microwave safe? And is it really that safe?

The microwave oven works on the principle of heating, in particular, water molecules by means of electromagnetic radiation with a frequency of 2.45 GHz. Water is a polar molecule, ie. that it behaves like a magnetic dipole when inserted into a homogeneous magnetic field. High-frequency oscillating microwave radiation causes the polar molecule to spin very quickly. The kinetic energy quickly changes to heat and this is transferred to the surrounding atoms. The water molecules in the food are heated in a microwave oven. However, the principle of a microwave oven does not guarantee its safety.^[1]

One of the concerns is that microwaves pass through the door of the turned on microwave, because visible light obviously passes through the door, affecting us. The fact is that there is a metal grid on the door that reflects the microwaves. The wavelength of radiation in a microwave is about 12 cm, while the wavelength of light is 390 to 760 nm. So microwaves can't pass through the door. However, it is true that a negligible part of the microwave radiation gets through the door, however, the negative effect on humans is zero.^[2]

So if the microwave radiation is reflected from the walls of the microwave, doesn't that mean that the microwaves remain in the microwave oven even after it has been switched off and can affect us when the door is opened? In fact, microwaves do not reflect 100%. Some of them are absorbed in the wall. When you turn off the microwave, the generated microwave radiation is absorbed within 10 ms. During that time, no one has a chance to even open the oven door.^[2]

Another concern is that microwaves acting on food in food stimulate unwanted chemical processes. However, microwaves do not fall into the category of ionizing radiation, so they do not have the energy to break molecules. The energy of microwave radiation is even much less than the energy of visible light, which we are also not afraid of. But this fear is not completely odd in the end. Heat in heated food causes the loss of some nutrients, such as vitamins. But the real thing is that the same side effect is achieved by conventional cooking. Heating in a conventional microwave oven is even slightly healthier because it is not possible to reach a temperature higher than 100 °C, which does not produce, for example, some carcinogenic compounds as in a conventional oven or pan. Of course, this does not apply to microwave ovens with a built-in grill.^[2]

But what needs to be mentioned in the end is that the microwave oven has certain pitfalls that need to be considered. One of them is uneven heating caused by standing waves. As we all know, heated food from the microwave is hot in some places and cold in some. This can be dangerous, for example, if the chicken containing salmonellosis is insufficiently heated. There is also a risk of burns, especially for children, where a relatively cold container may contain a very hot drink. It is also dangerous to put thin metal slices in the microwave, for example on decorative plates, because they cannot quickly dissipate the heat generated.^[2]