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My coworker said that microwaves are bad for you and you should avoid using them. As evidence she stated that if you microwave dirt nothing will grow in the dirt, so microwaved food is similarly hazardous to your health. Is this true?- JK, Burlington, VT

Let’s ignore that fact that our coworker is microwaving dirt for some reason and talk about microwaves and microwave ovens!

Let’s start with the waves themselves. Microwaves are a form of electromagnetic radiation. While the term “radiation” scares some people, this is context it describes everything from radio waves to visible light to gamma rays.  All electromagnetic waves have energy, but the amount of energy they posses depends on their wavelength. Gamma and X rays have the shortest wavelength and therefore the most energy, and these can hurt you. They can cause cancer at low levels and at very high levels (or doses), they can be fatal in just a few days.

Luckily, our atmosphere filters out most of the gamma and x ray wavelengths coming from space. However, lower wavelength light from the sun does make it to the surface of the earth in the form of ultraviolet (UV) and visible light. UV light, which has a shorter wavelength than visible light (and hence more energy) can be dangerous – it causes cancer over time as well, though all animals have adapted a system for repairing the damage it causes to our DNA that takes care of most of the damage. If the “dose” of UV light is high enough, it will burn you – something most of us have experienced as a sunburn.

The wavelengths of light below UV and visible light that are emitted by our sun (and other sources in space) do not cause cancer – they simply don’t contain enough energy to damage DNA. However, they can be immensely useful for things like radar, cellphones, radio, and our friend the microwave. Humans have figured out how to produce elecromagnetic radiation of all wavelengths ourselves, including the longer wavelength, lower energy forms. By making these wave ourselves, we are capable of producing large amounts of them – increasing the “dose”. One example of this is infrared light, which is a lower wavelength than visible light, but when produced at high levels is used to keep food warm in some fast food restaurants.

Microwaves are another example of this. They have even less energy than infrared – close to that of radio waves. In fact, they are commonly used in cell phone, satellite, and radio relay communications, as well as radar. Unlike radio waves, microwaves don’t travel through objects very well, so they are most useful for communicating between places with no obstructions in between, like from space to the earth, over shorter distances on land or for wireless devices like the bluetooth on your phone or other electronic devices. Microwaves are everywhere – they are literally hitting you right now.

How do microwave ovens cook?

In order to heat something with microwaves, you need a lot of them – much more than your cell phone can produce. In the 1970’s scientists figured out how to do this using a device called a magnetron. Every microwave oven contains a magnetron, and it uses the electricity from your power outlet to produce large amounts of microwaves. The inside of your microwave oven contains a metal box which reflects the microwaves around, allowing them to hit the food inside from many different angles, and most microwave ovens also rotate the food inside to change the angle that the microwaves hit the food.

Microwave ovens heat food by traveling into them and causing the molecules inside to vibrate rapidly. This vibration produces heat. Because they are relatively weak, microwave ovens can only travel about 1 inch into food, which is why the center of larger food items is sometimes cold. Another reason that microwaves often heat unevenly is that the degree of heat is impacted by the amount of water in the food (more water produces more heat), and also the amount of salt in the food – the salty parts of the food will heat up faster.

Are microwave ovens safe?

Yes, totally safe. High doses of microwaves could certainly be harmful if you were exposed to them – they could “cook” your skin (but not your internal organs, it can’t penetrate this far) just like they do to food. However, in order to be exposed to enough microwaves to hurt you, a person would have to try really hard. Microwave ovens do not release significant amounts of microwaves because they are shielded by the metal box inside, so if you were deadset on microwaving yourself, you’d have to disable the safety mechanism on the door so it would run with the door open and stick a part of your inside the oven. This would definitely be dangerous. Don’t do this.

Some people claim that microwave radiation can cause cancer. This is also untrue. Micowaves are a form of non-ionizing radiation, meaning they don’t have enough energy to ionize the molecules in your body, which is the event that causes cancer when you are exposed to x rays or UV light. Studies investigating the effects of microwave exposure have found no significant link to increased cancer risk.

Is microwaved food safe?

Of course it is. Microwaves are just waves of energy. The only thing they “leave behind” after they cook your food is the heat. There is no “radiation” or anything else that could harm you in the food after it is heated by microwaves. It’s just like shining a light on your food. The only difference before and after putting food in the microwave is that it’s warm afterwards.

As it turns out, the same is true for the more dangerous high energy, short wavelength ionizing radiation. Gamma and x rays can be passed through your food and will not leave behind anything “radioactive” or toxic. How do we know this? Because much of the food you eat has been exposed to gamma and x rays! This is done to kill harmful bacteria and viruses that could lurk in our food and might cause serious illness. In the United States, meat, fruit, vegetables, herbs, flour, and many other things are irradiated in this way. You eat these irradiated foods every day. They are perfectly safe.

If you were to microwave some dirt and plant some seeds in it, the seeds will grow just fine. Again, all you are doing is heating up the soil. If you heat the dirt for a very long period of time, you might break down some of the nutrients in the soil, but probably not enough to stop plants from growing. As it turns out, microwaving food is not worse then other methods of cooking at destroying vitamins anyway.

What’s the bottom line?

Microwaves and microwave ovens probably get a bad name because of the word “radiation” in electromagnetic radiation. People hear this word and think of radioactivity. Microwaves are not radioactive, and they will not turn your food radioactive. Go ahead and microwave your food without worries. However, we do not recommend microwaving dirt. That’s just weird.