As a physics graduate my family has sent me dozens of questions ranging from “Is the Mandela Effect real?” (not a physics question) to “Why did my Corningware dish explode in the oven?” (definitely a physics question).

Hands down the most common question I get is whether it’s safe to use a microwave oven to heat food. There are two sub-questions involved here:

1. Is it safe to eat food that has been radiated by microwaves?
2. Is it safe to stand in front of the microwave oven when it’s operating?

Before we dive in to these questions, let’s start with a (very short!) physics review.

Electromagnetic Radiation

Microwaves are electromagnetic radiation.

The full electromagnetic spectrum includes everything from low-energy radio waves, through to visible light, and up to high-energy gamma rays. Light travels in little packets called photons that have a particular wavelength (or frequency — they’re directly related). The shorter the photon’s wavelength (or equivalently, the higher its frequency), the higher its energy.

Humans can only see a small section of the electromagnetic spectrum, and we call that range of wavelengths ‘visible light.’ Electromagnetic radiation above that energy, specifically ionizing radiation, we know can be dangerous:

• Gamma rays (we greatly limit exposure to radioactive matter!)
• X-rays (doctors and dentists cover your body in a lead vest!)
• Ultraviolet radiation (we wear sunscreen!)

Most electromagnetic radiation with energy below the visible light spectrum we know is non-ionizing radiation:

• Infrared radiation (heat from the sun, your fireplace, your radiator)
• Microwaves (used to heat our food and to generate the image the body in an MRI)
• Radio waves (we transmit and receive signals at varying frequencies)

Okay! Physics lesson over. I promised it would be short! Now on to the main event…

Is it safe to use a microwave oven?

Yes.

Microwaves are low-energy photons that don’t harm humans the way high-energy photons do. Ionizing radiation is dangerous because it has enough energy to detach electrons from their atoms or molecules. This ionization can damage our cells, and in particular, our DNA molecules.

Microwaves do not have enough energy to ionize human DNA.

Is it safe to eat food that has been radiated by microwaves?

Yes.

Think about all the water molecules in your food as little magnets with a N and S pole. The oscillating waves align the polar moment of the water molecules N and then S and back again, over and over. This motion creates friction and the heat that warms your food.

The food you put in the microwave comes out as exactly the same food, just warmer.

Disclaimer: it’s important to consider the container you’re heating the food in. Plastics, even FDA-approved plastics, release massive amounts of particles when heated.

Is it safe to stand in front of the microwave oven when it’s operating?

Although microwaves do not have enough energy to ionize human DNA, they could cause damage by heating your tissues.

For this reason, only minimal leakage of microwaves is permitted under federal regulations. Microwave ovens are engineered to focus the radiation into the centre of the cooking chamber using waveguides. Microwave ovens also have a Faraday Cage, a metal enclosure that is designed to block specific frequencies of electromagnetic radiation. For example, the 2.45 GHz frequency produced by most commercial microwave ovens.

Fun fact: The leakage from your microwave oven might mess with your 2.50 GHz WiFi signal while cooking food, a good reason to use your 5 GHz Wifi frequency!

For a great demonstration of the Faraday Cages on microwave ovens, check out one of my favourite Physics Girl videos.

Why are so many people concerned about their microwave ovens?

My guess is that people are concerned by the word “radiation.”

Scientists, and physicists in particular, have a long history of having their terminology sensationalized in pop culture. The term radiation became well known after two devastating events: the atomic bombs used in WWII, and the disaster at Chernobyl nuclear power plant. You know that not all electromagntic radiation is damaging to our bodies. Still, the term radiation became associated with the damaging kinds — ionizing radiation.

People will even use misleading terminology like “put it in the microwave to nuke it!” even though we are not using nuclear fusion, fission, or ionizing radiation in a microwave! Talk about confusing.

So go forth and reheat that cup of coffee you let get cold. Just be sure to use a non-plastic container!