We’re all taught as children that washing our hands is the best way to stave off disease. But if you use a hand dryer in a public restroom after cleaning up, you’re actually doing more harm than good.
According to a new study from the University of Connecticut, hot-air dryers do suck in bacteria and other spores loitering in the bathroom. But when the next person uses the dryer, that same bacteria is sucked back out again onto “clean” hands.
The paper was published this week in Applied and Environmental Microbiology.
Researchers placed bacteria food on Petri dishes in 36 bathrooms in UConn health and science buildings to see how often bacteria would land on the plates. When the dryers were off, there was only about one bacterial landing every two minutes.
But when the dryers were on for 30 seconds, an average of 18 to 60 bacteria appeared on the dishes. These numbers were far higher in some cases–at one point, 254 bacteria landed on a plate in less than a minute.
And thanks to the airflow from the dryers, when people opened the door, the redistributed bacteria was spread throughout the whole building.
“Wherever there are people, there are gonna be bacteria,” study author Dr. Peter Setlow, a professor of molecular biology and biophysics at UConn, told Observer.
In all, researchers found 62 diverse types of bacteria from 21 species. One of them was Staphylococcus aureus, a common bacterium associated with everything from food poisoning to respiratory infections.
Those germs don’t just originate from the dryers—they may also come from toilet flushes since public toilets rarely have lids. Other activities like blowing noses and wiping feces could also contribute.
More serious diseases can also fester on these bathroom surfaces. The authors note that spores from flushing toilets often carry Clostridium difficile, a bacteria which causes explosive diarrhea.
“We kept following our noses and finding more,” Setlow said.
The study focused on warm air hand dryers rather than the jet dryers made by companies like Dyson. But these devices actually may be worse for overall health—a 2016 study found that Dyson dryers produced 60 times more bacteria than warm air dryers. Not surprisingly, Dyson has disputed the study.
One possible solution to many of these issues is installing HEPA filters in hand dryers. When the UConn researchers did this, the number of bacteria reduced four-fold.
The pathogens did not disappear completely, however. So the most hygienic course of action may be to step back in time and use paper towels. Despite their environmental effects, these towels still achieve 90 percent dryness in 10 seconds.
UConn has actually added paper towel dispensers to all of the bathrooms included in the study. So if it’s good enough for scientists, it’s good enough for you.