Hand dryers are generally considered to be sanitary, with the relative lack of contact with the surfaces in public bathrooms.

But the dryers, through movement of air alone, deposit fecal bacteria on surfaces like human skin, according to a new study in the journal Applied and Environmental Microbiology.

“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,” they write.

The University of Connecticut researchers exposed plates to the various kinds of air, and determined the total amount of bacteria, and a subset of spore-forming colonies of Bacillus subtilis PS533, found in the human gut and fecal matter, according to the study.

The ones exposed to the hot dryer air for 30 seconds averaged between 18 and 60 colonies.

The plates exposed only to ambient air without hand dryers engaged had less than 1 colony.

Those exposed to air moved by a small fan for 20 minutes averaged between 12 and 15 colonies per plate.

At the same time, the interior of the hand dryer nozzle had minimal bacterial detected, they add.

The spore-forming colonies of B. subtilis strains averaged only up to 5 percent of the bacteria sampled on the plates.

Retrofitting the hand dryers with HEPA filters reduced the bacteria on the plates four-fold, they report. However, bacteria still remained.

The study is not the first to identify hand dryers as a source of bacteria. A team of scientists at the University of Lees looking at airborne counts found that such appliances collected 27 times the germs that paper-towel dispensers did. They presented their research in the Journal of Hospital Infection.