Can Microwaves Kill Bacteria?

Since their debut, microwave ovens have become a common household appliance all across the US, with their ability to quickly heat simple meals, revive and reheat leftovers, defrost meat, pop popcorn and more. Despite their ubiquity, there’s been loads of confusion, misunderstanding and myths surrounding how microwaves operate.

Common tidbits of microwave misinformation include the idea that they’re dangerous to stand near, that they can cause cancer – or, as we’re about to discuss here, that microwave-cooked or warmed food is safer because the appliances zap bacteria with their radiation. Read on to discover whether or not the latter is the case, and for some tips for keeping your microwave bacteria-free.

Do microwaves kill bacteria?

Microwaves, as in the non-ionising radiation generated by your appliance, will not kill bacteria, in and of themselves. However, what microwaves will do is agitate particles in your food – namely water, sugar and fat molecules – thereby generating heat. By generating sufficient heat your microwave oven will, like any other cooking method, cause your food to reach a temperature at which bacteria cannot survive.

That said, there are some things you’ll need to consider when cooking with a microwave, if you want to thoroughly tackle bacteria and avoid nasties such as E. coli and salmonella.

First, due to irregularities in the shape, size or thickness of the food item you’re cooking, your microwave may cook unevenly. When your food comes out of the microwave, it’s important to check that there are no cold spots in your food, which may still host live bacteria. To avoid cold spots, it’s important to give your food a stir, or turn it over, part way through cooking and ensure food is cooked for long enough so that it’s piping hot all the way through.

Second, a microwave oven heats food from the inside out using wave radiation. As such, the interior surfaces of the microwave won’t reach the same high temperatures as a standard oven or an air fryer, and can therefore play host to bacteria. For example, meat juices, crumbs and other food spills on the interior walls of your microwave can cause all sorts of bacteria to thrive.

To prevent this from happening, make sure you clean and disinfect your microwave regularly. You can also mitigate spillages and spatter by placing food on a plate or in a microwave-safe container, as opposed to stand-alone, and covering it appropriately.

To learn more about how microwaves work, check out our full article. If you have any other concerns about microwaves safety, you can also read our ‘Are Microwaves Bad For You?’ explainer, which looks at some myths and misunderstandings surrounding microwaves, while also offering tips to solve any issues you might be having with your appliance.