The study, conducted by researchers at the University of Connecticut School of Medicine and recently published in the journal Applied and Environmental Microbiology, determined that air-blowing hand dryers were essentially shooting out plumes of bacteria-infested (read: feces-filled) air onto people's hands and into the surrounding air -- even beyond the walls of the bathrooms where they were installed. Gross, right?
To figure this out, researchers tested hand dryers in three different on-campus public restrooms, exposing 36 different glucose-coated plates to the air, first with the air dryers off and then with air dryers in use. What they found was that when the air dryers weren't in use the air produced a relatively small six colonies of bacteria per plate on average, but when they were in use, nearly 60 colonies of bacteria, on average, grew on each plate. Among the microbes reserachers spotted on the air dryer-affected plates were some that are found in human poop.
To determine the excessive bacteria wasn't originating in the blowers themselves, the researchers also swabbed inside the machines before use and found that there wasn't nearly enough to account for the numbers they found on the plates.
So, what does this all mean? Well, essentially it helps confirm what previous studies have suggested: that air-blowing hand dryers in public restrooms suck in tons of poop particles whizzing around in public restroom air (thanks to lidless flushing, etc.), and then blow it out, presumably both onto the hands of unsuspecting hand-washers and into the air in general. However, unlike some other, occasionally contentious studies that've suggested people use paper towels instead, the researchers involved in this one suggested also fitting hand dryers with HEPA filters, which could significantly reduce the amount of bacteria that ends up on your hands.
Bottom line: public restrooms are nasty, and unless you're lounging in a hazmat suit you probably can't escape the grasp of at least a few crappy germs when you use one.
h/t Live Science