Your Microwave Is Teeming With Bacteria, Study Suggests

You’ve heard of the gut microbiome—the community of bacteria, viruses and fungi that help keep humans and other animals healthy. But what about the microwave microbiome?

New research finds that microwave ovens are hosts to their own distinct communities of microbes, whether in home kitchens or office spaces. Many of these microorganisms can survive the radiation that warms food, challenging the long-held belief that microwaves successfully kill bacteria that may be harmful to human health.

Researchers described their findings in a new paper published Wednesday in the journal Frontiers in Microbiology.

Home cooks shouldn’t panic, however—their microwaves likely aren’t any dirtier than any other parts of the kitchen. However, the findings should serve as a reminder that these appliances need to be cleaned regularly, too.

“A microwave is not a pure, pristine place,” says study co-author Manuel Porcar, a microbiologist at the University of Valencia in Spain, to Nature News’ Alix Soliman.

Past studies have found microbiomes in other household appliances, including coffee makers and dishwashers. But researchers were curious to know whether the same communities exist inside microwave ovens, which use invisible electromagnetic waves to excite water molecules inside foods. As the molecules vibrate, they produce heat.

The team swabbed the insides of 30 microwaves in homes, scientific laboratories and shared kitchens, such as in office spaces and cafeterias. Then, they cultured their samples and waited to see which, if any, microorganisms flourished. They also sequenced the DNA in their samples.

In the end, they cultivated 101 strains from the samples, representing 747 different genera of bacteria. Many were strains that are often found on human skin, and a few were known to cause food-borne illnesses.

As suspected, each microwave’s location affected its microbiome. For instance, microwaves used in laboratories had the most diverse bacteria—including “extremophiles,” or microbes that can withstand harsh conditions.

“We hypothesize that microwaves actually select, from the pool of bacteria present in the air and surfaces, those able to resist radiation,” Porcar tells Newsweek’s Pandora Dewan.

The discovery of extremophiles in microwaves is not all that surprising, given that they can live in “almost any extreme-exposure environment,” says Belinda Ferrari, a microbiologist at the University of New South Wales in Australia who was not involved in the research, to New Scientist’s James Woodford. Extremophiles have been found in hydrothermal vents, inside Earth’s crust, on Antarctica, in the stratosphere and beyond.

“They can adapt to everything,” she adds.

Those hardy microorganisms dwelling in microwaves could have other possible uses, such as cleaning up toxic waste, per Nature News.

In the future, the team hopes to explore how extremophiles evolve within microwaves over time. Another possible experiment might involve sampling microwaves both before and after cleaning, Ferrari suggests to New Scientist.

But for now, microwave users might want to brush up on their cleaning skills.

“We recommend regularly disinfecting microwaves with a diluted bleach solution or a commercially available disinfectant spray,” says study co-author Daniel Torrent, a researcher at the biotechnology startup Darwin Bioprospecting Excellence SL, in a statement. “In addition, it is important to wipe down the interior surfaces with a damp cloth after each use to remove any residue and to clean up spills immediately to prevent the growth of bacteria.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.