PSA: More Than 700 Kinds of Heat-Resistant Bacteria Could Be Living in Your Microwave — Here’s What to Know

Microwaves are notorious havens for food splatters and other residue, but it turns out they can also harbor a slew of bacteria that are resistant to heat, too. 

That’s the conclusion of a surprising new research published in the journal Frontiers in Microbiology. For the study, researchers swabbed 30 microwaves in households, offices, and microbiology laboratories, and cultured the results to see what happened. From there, they analyzed the DNA of the microbes they found. 

Overall, the researchers found 747 kinds of bacteria, although the types varied by where the microwaves were located. Home microwaves contained bacteria like Staphylococcus, which can cause a range of infections in people. The kitchen microwaves also had more microbes than the others, although the microwaves in labs had a more diverse range of bacteria. 

Microwave-resistant bacteria in close contact with your food sounds like a recipe for disaster, but microbiologists say it’s not as scary as it seems at first glance. Here’s what they want you to know. 

How can bacteria survive in the microwave?

First, it’s important to go over how microwaves work. These appliances heat things up by vibrating water molecules inside food, says Donald Schaffner, Ph.D., a microbial risk assessment and cross contamination expert at Rutgers University. This produces heat and typically will kill bacteria that may be lurking inside. But, of course, nothing is perfect. 

Home microwaves heat items unevenly, which means that some locations in food will receive higher heat than others, explains Ahmed Yousef, Ph.D., professor of food microbiology at The Ohio State University. As a result, if something splatters out of the container you’re heating food or liquid in, it may contain bacteria. 

The water content in the food matters, too. “The drier the food, the less likely to be heated by microwave energy,” Yousef says. “Even popcorn has some water inside the kernels. Without that water, it would not pop in the microwave oven.”

Microorganisms that wind up in the microwave usually get there from food you put inside, and may come off with splashes and splatters as the food cooks, Yousef says. “Most of the splashing will land on the walls, corners, or even the ceiling of the unit,” he continues. “These locations are not designed to receive the microwave energy; the center is where most of the energy goes. Therefore, microorganisms in these off locations would survive for some time.”

Unfortunately, the drier those particles get with time, the harder it is to kill any bacteria inside, even when they’re regularly nuked by a microwave, Yousef says. 

Can microwave bacteria contaminate your food?

That’s up for debate. “Certainly, if a microorganism is sitting inside the oven cavity of a microwave, it’s very unlikely to be able to jump from there to get into food,” Schaffner says. Meaning, if the food you’re heating up is inside a glass container or on a plate, you’re likely OK.

But if you heat foods up by placing them directly onto your microwave’s turntable, this could be a potential issue. 

What can happen if you ingest microwave-friendly bacteria?

It depends on the type of bacteria, which tends to be linked to the type of food you’re heating up, Yousef says. “I would worry about spilled milk, soup, or stew, because these nutritious foods are also good for growing microorganisms,” he says. 

But even if microorganisms end up in your food, Schaffner says you’ll likely be OK. “Both genera of potential foodborne pathogens — Bacillus and Staphylococcus — need high levels of the microorganism to be present before any significant risk to human health,” he explains. So, while there is a definite ick factor, the small amount of either bacteria that may be lurking on the walls of your microwave or on the turntable is probably not going to make you sick. 

“I’m really not worried about getting my food contaminated from anything that might be inside a microwave,” Schaffner adds. 

How to minimize microwave bacteria in your food

There are a few things you can do to lower the risk you’ll have heat-resistant bacteria lurking in your microwave. One is to do your best to minimize splatters and spills. “Cover food — vent holes may be needed — but cover so the food doesn’t explode out of the container,” says Janet L. Buffer, M.P.H., R.D., senior institute manager at the Institute for Food Safety and Nutrition Security at The George Washington University. “Covering food will also reduce the potential for contamination.” 

It’s admittedly a pain, but doing your best to clean your microwave regularly is also important, Buffer says. “Spills and explosions should be cleaned up immediately using warm soapy water and rinsed with clean water,” she says. “An antibacterial cleaner is an added benefit, but typically, the antimicrobial cleaner must be applied after the equipment is washed and then rinsed.”

Yousef also stresses the importance of being on top of your microwave hygiene. “If we clean spills as soon as they happen, and do daily cleaning or checking to make sure no food residues are accumulating in the microwave, I see no harm,” he says.