Hot-air hand dryers may be spewing other folks’ bacteria onto your freshly washed hands.
A study published online in the journal Applied and Environmental Microbiology found that air blowing from hot-air hand dryers is germ-ridden.
The findings
Researchers used petri dishes to test for bacteria in the restrooms of the University of Connecticut School of Medicine.
They found that an average of one bacteria colony or less grew on each petri dish that was exposed to bathroom air for two minutes. Yet an average of 18 to 60 colonies grew on each dish that was exposed to air from hand dryers for 30 seconds.
They also found that adding high-efficiency particulate air (HEPA) filters to hand dryers reduced the amount of bacteria they blew onto petri dishes by about four-fold — or about 75 percent.
Further, when researchers swabbed the inner surfaces of hand dryer nozzles, they found relatively few bacteria colonies — about four per bathroom, on average.
The source of bacteria
These findings suggest that most if not all of the bacteria spewed by hot-air hand dryers comes from bathroom air, according to the study.
In other words, bacteria are being sucked into dryers from the air, not multiplying within dryers. Researchers suspect the bacteria are “either passing through hand dryers without HEPA filters, or pulled into the air coming out of hand dryer nozzles by convection,” the study states.
As for how bacteria gets into bathroom air to begin with, I’ll leave the explanation to John Ross, an assistant professor of medicine at Harvard Medical School and a medical doctor who is board-certified in infectious disease.
Ross is not among the study’s authors but wrote about the study in the Harvard Health Blog:
“Unfortunately, every time a lidless toilet is flushed, it aerosolizes a fine mist of microbes. This fecal cloud may disperse over an area as large as 6 square meters (65 square feet).”
The good news
Ross reports that one type of bacteria the study found in restrooms, Staphylococcus aureus, causes disease in people who are healthy.
According to the U.S. Library of Medicine, Staphylococcus aureus causes most staph infections, which most commonly include skin infections but also include illnesses like pneumonia.
None of the other types of bacteria the study found in restrooms causes disease in healthy folks, however. In fact, Ross says you’re more likely to catch an infection through contact with other people than with restrooms.
Just reach for the more hygienic drying option of paper towels when possible, and dry well.
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