I live in a very small space and have an old Kenmore microwave/convection oven that I’ve been cooking in for years. This oven came with my home and I have no way of knowing if it is older than my adult children, but I suspect it may be.  Over the years I’ve wondered about the safety of microwaves, mine in particular, but hadn’t taken the opportunity to do the research. In preparing to write this blog I took a look at dozens of websites, articles and studies. Quite honestly, I approached the topic prepared to toss my microwave, there has simply been so much negative press over the years. I thought it would be an open and shut case. I am going to have to jettison the old machine, but not for the reasons I expected.


Microwave ovens heat food through the use of electromagnetic radiation. The waves emitted by the ovens cause polar particles (like water) in our food to flip back and forth, causing friction (heat) that results in the heating/cooking of our food. Because the microwaves can penetrate (and heat) objects to the depth of a few centimeters, it’s important that they stay within the confines of the oven. This is accomplished through use of the screen in the glass that you can see as well as the latching mechanism in the door. As long as the microwave is relatively new and in good condition, the radioactive frequency emitted should be very little (less than 5mW/cm2,which is the upper safe limit set by the FDA for the general public). The wave-length of microwaves are way too large to fit through the screen in the door – so unless this is damaged, the microwaves themselves cannot escape in this manner. You are far likelier to have issues with gaps around the door – which is where you could have significant leaks if the seals have become damaged over time. These waves are only a danger if they escape during use. Once the microwave is turned off, the waves completely cease.

Aside from radiation leakage, the most common dangers associated with microwave use are uneven heating, burns caused by spilling/splashing the contents as they come out of the oven and superheating of liquids. Superheating (especially with water) can occur when you boil water in the microwave in an unblemished glass container, and cause turbulence after the heating is complete. When you open the microwave and introduce motion or a metal spoon – rapid boiling can occur where there was none. Scary! Microwaving with a wooden spoon is an option if you choose to boil water, as the pores of the wood introduce something called nucleation sites. These sites give bubbles a place to form and heat to escape so they do not spontaneously form, seemingly from nowhere.

Another area of potential danger that most of us are aware of is the transfer of chemicals from the packaging or containers used to heat the food in.  This is true for any packaged food, but is worse for foods that are heated or frozen, particularly when there is fat in the food.  When you buy packaged foods designed for microwave heating, we highly recommend transferring it to glass or ceramic and tossing the package.  Even better, don’t buy microwavable meals.  

What about the nutrition of the food that’s been cooked in the microwave? How does this differ from other methods? Some arguments against that I ran across during my travels through various opinions discussed how microwave cooking denatures proteins and alters the molecular structure. Louis Bloomberg, a professor of physics at the University of Virginia has a great explanation: “Microwaves don’t affect the molecular structure of the food, except through the thermal effects we associate with normal cooking (e.g., denaturing of proteins with heat and caramelizing of sugars). That’s because, like all electromagnetic waves, microwaves are emitted and absorbed as particles called “photons.” The energy in a microwave photon is so tiny that it can’t cause any chemical rearrangement in a molecule. Instead, it can only add a tiny amount of heat to a water molecule.”1(for more info, take a look at the complete quote here.) While there is a lot of theorizing about how microwave cooking rips apart and rearranges molecules into very dangerous forms, I could find no good research to substantiate this. However, because there is no research does not mean it’s safe or good.  Therefore, we recommend maximum microwaving to be no longer than three minutes.  This means no defrosting in the microwave or cooking baked potatoes in there.

It turns out microwave cooking (steaming) can rival baking when it comes to retaining the antioxidant activity of many vegetables.2 The microwave is a very efficient and quick tool for accomplishing this. The key here is to avoid cooking the vegetables in additional water, which is the main culprit for nutrient loss regardless of how the veggies are cooked.

Aside from the above mentioned, a lot of folks weighed in about how microwaved food doesn’t taste as good as its conventionally cooked counterparts, which may very well be the case especially for certain things. This is definitely worth of consideration – and a matter of opinion.

I use mine for reheating coffee, leftovers, and occasionally melting butter. My oven functions as both a microwave and a convection oven, which is a 2 in 1 solution – great when space is at a premium. My take away from everything I’ve read is that I do need to investigate newer equipment, and I will likely replace my oven with a newer version (these are now available with a broiler feature. Bonus!) Three things I will do now are the following:  never microwave foods longer than three minutes, transfer any food from a temporary packaging to glass or ceramic, and continue to stand away from the oven when using it on the microwave setting.  

Late in the process of researching for this post I ran across this article that provides links to many of the studies I looked at in my search for the most current truth. Feel free to link out to learn more.

By Samantha, Bastyr Intern


  1. “How Everything Works – Question 690”. Howeverythingworks.org. N.p., 2016. Web. 24 July 2016.
  1. Jiménez-Monreal A, García-Diz L, Martínez-Tomé M, Mariscal M, Murcia M. Influence of Cooking Methods on Antioxidant Activity of Vegetables. Journal of Food Science. 2009;74(3):H97-H103. doi:10.1111/j.1750-3841.2009.01091.x.