If you use a hot-air hand dryer after washing your hands, you may want to rethink that. A study published in Applied and Environmental Microbiology in February claims that hand dryers actually spray fecal matter all over your clean hands.
Scientists compared the bacteria found in the air from hand dryers to air in a bathroom.
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According to an abstract, scientists exposed a plate to a hand dryer for 30 seconds and saw an average of 18 to 60 colonies of bacteria per plate.
The plates exposed to the bathroom air for two minutes with the hand dryers off averaged less than 1 colony per plate, and plates exposed to bathroom air for 20 minutes with air moved by a small fan had 15 to 12 colonies per plate. The bathroom air samples returned substantially fewer colonies than the hand dryer sample.
Researchers found that "many kinds of bacteria, including potential pathogens and spores, can be deposited on hands exposed to bathroom hand dryers."
Additionally, "spores could be dispersed throughout buildings and deposited on hands by hand dryers."
The study was unable to conclude if hand dryers were a reservoir for bacteria, or if they just blew "large amounts of bacterially contaminated air."