Hand dryers in public restrooms that blast bathroom air onto your recently washed hands can deposit bacteria, a recent study has found.
Published in the April 2018 issue of the journal Applied and Environmental Microbiology, the study looked at 36 men’s and women’s bathrooms at the University of Connecticut School of Medicine, according to Business Insider.
Researchers measured how much bacteria was deposited on plates left in the restrooms, and they found far more bacteria appeared on plates exposed to hand dryers for 30 seconds than the plates that were left exposed to regular bathroom air.
Plates placed in contact with hand dryer air had 18 to 60 colonies of bacteria each, while those left open to restroom air averaged less than one colony each.
“The more air ya move? The more bacteria stick,” biochemist and study author Peter Setlow told Business Insider. “And there are a lot of bacteria in bathrooms.”
Even plates that were left exposed to air moved around by a small bathroom fan – for 20 minutes – had less bacteria than the hand-dryer plates. The fan-exposed plates had averages of 15 and 12 colonies in two buildings that were tested.
Since completing the study, Setlow has stopped using hand dryers, he told Business Insider.
There’s evidence that bacteria moved by hand dryers could be deposited on just-washed hands, the abstract for the study indicates.
“These results indicate that many kinds of bacteria, including potential pathogens and spores, can be deposited on hands exposed to bathroom hand dryers, and that spores could be dispersed throughout buildings and deposited on hands by hand dryers,” the abstract states.
The researchers found that dryers that were fitted with HEPA filters saw around a fourfold reduction in bacteria, and the authors say their study has implications for control of bacteria in public settings, including health care facilities.
It’s not completely clear if the dryers act as a reservoir for bacteria or if they’re just blowing contaminated air around. The interior of the dryers’ nozzles showed minimal bacteria.
A 2016 study in Saudi Arabia similarly found that hot air dryers can “deposit pathogenic bacteria onto the hands and body of users,” according to the abstract of the paper in the Saudi Journal of Biological Sciences.
“Bacteria are distributed into the general environment whenever dryers are running and could be inhaled by users and none-users alike,” the abstract stated.
And in 2011, a research review published in the Mayo Clinic Proceedings found that “from a hygiene viewpoint, paper towels are superior to electric air dryers.”