Hand dryers may leave your hands significantly more dirty than they were before being dried, a new study says.

Results of the study, published in the journal Applied and Environmental Microbiology, found that plates exposed to 30 seconds of a bathroom hand dryer gained at least 18 to 60 colonies of bacteria, while plates exposed to bathroom air for two minutes had fewer than one colony.

The authors concluded that the “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 study’s authors, who found that the nozzle of the dryers had minimal bacterial levels, said more evidence is needed to determine whether the dryers were bacteria harbors themselves or simply blew around large amounts of contaminated air.

It is known that bathroom air can contain fecal matter and droplets of urine.

The study noted that hand dryers equipped with high efficiency particulate air (HEPA) filters could reduce the bacteria fourfold.