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Don't worry, your dishwasher is not trying to kill you

No evidence was found that the presence of dishwasher fungi harmed anyone in the 189 households.
REUTERS/Scott Olson
No evidence was found that the presence of dishwasher fungi harmed anyone in the 189 households.

No, your dishwasher is not trying to kill you — despite last week’s press release headline that stated otherwise and the equally startling media headlines that continued with that theme.

My favorite: “The Killer Mutant Fungus in Your Dishwasher.”

Yes, a study about fungi in dishwashers will appear soon in the science journal Fungal Biology (published by the British Mycological Society). And, yes, the authors of that study did find that a large percentage of the dishwashers they tested harbored fungi, including two species of scary-sounding black yeasts.

Dana Davis
Dana Davis

But we needn’t panic or stop using our dishwashers, according to Dana Davis, an associate professor of microbiology at the University of Minnesota.

“I can’t see any reasons why this [study] should raise any warning bells at all,” he told me in a phone interview last week.

“There’s really no correlation between these dishwashers, the fungi and human health,” he added.

Seven fungi found
At first glance, the details from the study seem to paint a rather ominous picture. Teams of researchers from Slovenia, China and the Netherlands gathered samples from the rubber seals inside dishwashers from 189 private homes in 18 countries across six continents.

Some 62 percent of the seals tested positive for fungi (including all six of the seals on U.S. dishwashers). And 35 percent harbored one of two species of the black yeast Exophiala, which the authors call a “polyextremophile” organism because of its ability to survive in extreme conditions, including the near-boiling temperatures of a dishwasher. The other fungi that turned up on the dishwasher seals were more common species of Aspergillus, Candida, Magnusiomyces, Fusarium, Penicillium and Rhodotorula.

No evidence was found that the presence of these fungi harmed anyone in the 189 households, but the study’s authors call for more research to determine if the organisms could pose a health risk in the future, particularly since Exophiala seems so evolutionarily adaptive.

The fungi around us
Davis is not concerned. We already live in quite close quarters with fungi, he pointed out. “If you pull up your kitchen drain, there’s stuff growing on those seals,” he said. “There’s a lot of bacteria, but there’s fungi there, too.”

We should be more concerned with mold spores in our basements than with fungi on our dishwasher seals, he added.

Dr. Aaron Devries, a medical epidemiologist with the Minnesota Department of Health, agrees. The fungi identified in the study “are a widely distributed group of fungi found in soil, water, and many other diverse environments,” he wrote in an e-mail. “They make people sick only in circumstances where their immune system is highly affected such as persons who have received an organ transplant, bone marrow transplant or have a congenital disease affecting the immune system like cystic fibrosis. These individuals are given special instructions by their health-care provider on how to minimize their exposure to common organisms like these fungi.”

Keep moisture away
If you want to avoid fungi growing on your dishwasher seals, make sure your machine dries out thoroughly after each washing cycle. If moisture remains, you may want to wipe the seal with a dry cloth. Never use bleach in your dishwasher without first checking with the machine’s manufacturer — you could ruin its internal workings.

Davis, however, isn’t changing any of his household’s dishwashing routine. “I’m still going to let my son clean it out,” he said. “It’s his job to put away the silverware, and I’m still going to have him do it.”

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Comments (4)

“Never use bleach in your dishwasher without first checking with the machine’s manufacturer — you could ruin its internal workings.”

Maybe this explains something about dishwasher longevity – or the lack thereof. The gel I regularly use in my dishwasher lists only two ingredients: sodium silicate and chlorine bleach. Other brands have similar ingredient lists. Bleach is a common ingredient in many detergent mixes for automatic dishwashers.

Ray,

I believe those are OK (but check your user manual). My warning is against using liquid bleach inside the machine.

I'm curious as to whether the seals which are harboring the fungi are the seals around the door of the dishwasher, which are easily accessible, could be routinely disinfected, and are often neglected,...

Or are these the seals where the motor and pump are attached to the body of the dishwasher, which are generally inaccessible, and in some designs constantly sit in a pool of water at the bottom of machine.

If they are the pump/motor seals, it's likely a change in the design of the machine could lessen it's ability to harbor such fungi, which could lead to a real uptick in dishwasher sales as concerned people replace their dishwashers with new "fungi-free" or "fungi-resistant" designs.

Who sponsored this study, again?

Greg,

Samples were taken from the door seals.