Washing your hands after you use the bathroom is a good idea. But using a public dryer could undo all that hard work, according to a new study.
A study, published in the journal Applied and Environmental Microbiology, examined 36 men’s and women’s bathrooms at the University of Connecticut School of Medicine.
The researchers were searching for a strain of bacteria typically found in laboratory environments called Bacillus subtilis or PS533, which is harmless to humans, according to Newsweek.
The researchers tested for bacteria on plates held up to hand dryer air for 30 seconds and found that each plate held 18 to 60 colonies of bacteria per plate afterwards.
Not only did the team find PS5333 in each bathroom, they found evidence of other forms of bacteria that could be harmful to humans.
"Bacteria in bathrooms will come from feces, which can be aerosolized a bit when toilets, especially lidless toilets, are flushed," Setlow told Newsweek, adding that people move in and out the bathroom constantly and the germs they carry with them can add to the bathroom environment.
Fitting a dryer with high-efficiency particulate air, or HEPA, filter reduced the amount bacteria by about 75 percent, the researchers found.
However, the study concluded that there is less information on what specific kinds of bacteria are dispersed by the dryers. Researchers were also unsure if the bacteria comes from a "reservoir" in the dryer or if they just suck in and blow around a lot of contaminated air.
"The more air ya move? The more bacteria stick," Setlow told Business Insider . "And there are a lot of bacteria in bathrooms."
Setlow told Newsweek that after the study was over, he stopped using dryers. The University of Connecticut School of Medicine stocked its bathrooms with paper towels as well.