Let me be upfront: public restrooms have never ranked among my favorite spots, and a new study from my home state — the University of Connecticut (USA) and Quinnipiac University — may partly explain why. Is it possible that the hot-air dryers in these restrooms are drawing bacteria out of the air and blowing them onto the freshly washed hands of people who never see it coming?
To put this idea to the test, the researchers left petri dishes open to restroom air under varying conditions, then returned them to the microbiology lab to check for bacterial growth. Dishes exposed to bathroom air for two minutes with the dryers switched off produced just one bacterial colony — or none. By contrast, dishes placed in the hot air of a hand dryer for only 30 seconds yielded as many as 254 colonies (most, however, showed between 18 and 60 colonies).
So were the bacteria breeding inside the dryers, or were they simply being drawn in from the surrounding bathroom air? To find out, the team fitted the dryers with high-efficiency particulate air (HEPA) filters, which would strip most bacteria from the air moving through the device. When petri dishes were once again exposed to the dryer air, the bacterial count dropped by 75%. The researchers also detected only tiny amounts of bacteria on the dryer nozzles. Their conclusion: the bulk of the bacterial spray from the hand dryers originated in the washroom air itself.
How do those bacteria end up in the air to begin with? Sadly, each flush of a lidless toilet releases a fine aerosol mist of microbes. That fecal cloud can spread across an area as large as six square meters (65 square feet). In hospitals, such toilet aerosols may be a particularly concerning route of transmission.
Does the study offer any reassuring news? Yes — the great majority of the microbes detected do not sicken healthy people, with Staphylococcus aureus being the notable exception. Certain bathroom bacteria, such as Acinetobacter, cause infections only in hospitalized patients or those with weakened immune systems. The remaining organisms found are largely harmless. What's more, air in ordinary bathrooms may hold fewer bacteria than the restrooms studied here. Those sampled restrooms sat inside a university health sciences building, and at least some of the bacteria likely came from laboratory experiments conducted in the same building.
So what's the takeaway? Keep drying your hands — leaving them wet after washing actually helps bacteria linger on your skin. Paper towels are likely the most hygienic option, which is why they are already standard in health care settings. You may also want to steer clear of jet air dryers, which have likewise been linked to the spread of germs in restrooms.
Keep in mind, too, that your odds of catching a serious pathogen in a restroom remain low. Direct contact with other people is a far more likely way to pick up an infection.
I'm Dr. Michael Hunter. Thanks for reading today — please consider following this blog by signing up below. Thank you.
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I hold degrees from Harvard, Yale and the University of Pennsylvania, and I practice radiation oncology in the Seattle area.
https://www.health.harvard.edu/blog/the-bacterial-horror-of-the-hot-air-hand-dryer/
