Are microwave ovens safe?


I received a question from a smart and sassy older friend from San Diego, and I thought that her question and my answer would be interesting to our readers. I’ll call her by her initial, S, which also stands for smart and sassy. She’s not a technical person.

Am calling on your expertise … I belong to a “food group” that meets a couple times a month, usually viewing a health related video from KPBS, or other topic. The topic this week is going to be Microwaves. I have the feeling that it won’t be positive. I have used a microwave since the 70’s … mostly just heating or reheating … I remember in the early days there was concern about standing in front of the microwave and radiation or something escaping and causing health problems. How about rendering your opinion on this before I accept the invitation to attend this Sunday. I don’t want to listen to some ghastly report on all the negatives of microwave ovens.

So, do you have an opinion on the health safety of them?? I might go and share it ..

Dear S,

I have opinions about microwave ovens for cooking and about their safety. The radiation that comes from cell phones is also microwave radiation, but a thousand times lower power. In these matters, I count myself an expert, but not a specialist. What I have to say is general knowledge about fundamental and well-established physics.

You are welcome to share the next few paragraphs with your friends, and I’ve attached a copy of my paper about cell phones which you are also welcome to print and copy.

Microwaves are a form of electromagnetic radiation. Other forms of electromagnetic radiation are radio and TV signals, infrared (heat) radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. These differ from one another by the frequency at which the waves oscillate, and by the wave length of the waves. They all travel at the same speed, known as the speed of light, which is really fast: 186,000 miles each second. Microwaves oscillate in a range more or less a billion times per second, a billion Hertz, a gigaHertz. The wavelength of microwaves also is in a range more or less from a foot or so down to an inch or so.

All waves carry energy from one place to another. In a microwave oven, a doodad called a magnetron takes energy from your house electric wires and converts it into energy in the microwaves, and send this energy out into the oven. The stuff you want to cook or warm absorbs this energy and becomes hotter. When you broil a steak in your regular oven, the gas flames or the electric heating elements emit infrared radiation that carries energy from the flames or elements to the surface of the steak, where they deposit their energy. In the case of infrared, the energy goes into a thin layer at the surface, then in moves into the steak, by conduction. In the case of microwaves, the energy goes into a thicker layer, an inch or two thick. That layer warms, and the energy moves deeper into the frozen turkey or blueberry muffin.

In each case, or in any other form of oven cooking, the heat energy in the food is identical. The differences in baking, roasting, broiling, or microwave have to do with where the energy is deposited and how it moves within the food. None of this has any significant effect on the nutritional value of the food. But consider, for example, broiling. The heating elements deposit a great deal of energy in a thin layer, so the temperature of that layer gets very high. Various chemical reactions occur in that high temperature layer, browning and so on, that change the color and the taste. Microwaves don’t do that because the energy goes into a thick layer, so no part reaches such a high temperature. Since people like the taste of the chemicals that broiling produces, they might prefer broiling to microwaving.

Now, power is the rate at which energy moves around. We measure power in watts. Light bulbs use energy at a rate of 75 watts or 40 watts, and so on. A microwave oven typically produces about one thousand watts, a kilowatt. So this rapidly warms whatever absorbs that energy. Mostly, your body is capable of absorbing a kilowatt without much trouble, except that you’d start sweating. Just sitting at your desk, reading this e-mail, you produce energy, from your food, at 60 watts or 75 watts. If you exercise hard, you could produce a kilowatt, from your muscles. If someone were to beam a kilowatt of microwaves into you (and this experiment has been done) you’d sweat as much as if you were exercising that much. There are no ill effects from this. Your body has powerful means to keep its temperature constant as the environment and your activity vary.

But, there are a couple places in our bodies that do not have good cooling: the cornea and lens of our eyes, and testicles. The cornea and lens do not have blood vessels because they have to be transparent, thus the blood cannot carry away excess heat the way it does anywhere else in our bodies. This is why it would be a bad idea to check your microwave popcorn by putting your eyes close to the glass, screened door of the oven. No microwaves get out except a little through the door, and that doesn’t go far from the door. Testicles have cooling, and they like to be cooler than normal body temperature, which is why men and other animal males have those ludicrous, funny looking sacks attached, which is to help the contents remain cool (even when the owner is overheated).

As long as you are standing around in your kitchen, heating your tea water, popping your popcorn, thawing your TV dinner, you are entirely safe from harm from your microwave oven. Don’t disable the door interlock. Don’t drop the oven on your foot. But don’t worry about having one in your kitchen.

As for cell phones. While a microwave oven has a kilowatt inside the chamber, which stays there, a cell phone radiates about 1 watt outward to try to find the cell phone tower. That’s like one of those tiny Christmas tree lights that people string along their eaves. You absorb a fraction of this one watt, but your body can easily handle this. It causes only a tiny bit of heating, less than the temperature change in your body between early morning and late afternoon. There are no known health effects from this.

You sometimes hear scare stories about microwave ovens and about cell phones, cell phone towers, your computer’s WiFi, and so on. All of them are wrong. Don’t worry about these things.

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