Credit: Wikimedia Commons.

A lot of people cringe at the idea of visiting public restrooms but few have any qualms with hand dryers — after all, they just blow hot air and never come into direct contact with your body. However, you should know that they’re far from harmless. Researchers at the University of Connecticut analyzed the outflow of hand dryers in various public restrooms and found they were dispersing Bacillus subtilis, a bacteria commonly found in human feces, all over the room.

Debris, like dust and skin but also microbes, are constantly being circulated through a public restroom as people move in and out. Especially when a lidless toilet is flushed. Because hand dryers suck the ambient air in the restroom and then spew it out at high velocity, these machines actually expose you to more microbes — at least, that’s what a new study found after growing bacterial colonies collected from either bathroom air or blow dried air.

When the hand dryers were off, only six colonies on average grew per plate. However, with the blow dryers up and running, so were the bacteria: as many as 60 colonies, on average, grew per plate, as reported in the journal Applied and Environmental Microbiology. Overall, 62 types of various bacteria representing 21 species were identified by the researchers, including Staphylococcus aureus, which can sometimes cause serious infections.

The team of researchers investigated airborne bacteria in 36 bathrooms at the University of Connecticut School of Medicine. In every tested bathroom, the researchers discovered a lab-engineered strain of the common soil bacteria Bacillus subtilis called PS533. This strain is never found in nature and exclusively appears in laboratory settings. What happened was bacterial spores likely traveled from labs, either carried by air or people’s movements, to all sorts of other rooms in the research building, including bathrooms. The PS533 strain is totally harmless to humans but its presence in each and every one of the tested environments highlights just how easy it is for bacteria to spread.

The new findings are important for healthcare facilities and other environments where sanitation is king. However, for the most part, the new study shouldn’t worry anyone since our immune system can handle the kind of bacteria that’s blown on our hands and faces. And yes, there are ways to minimize restroom-bacteria exposure. The researchers found that adding high-efficiency particle air (HEPA) filters blocked 75% of the bacteria blown by the hand dryers — but that’s still not perfect. If you want to be extra safe, the best option to dry your freshly cleaned hands is also one of the simplest: use paper towels. Previously, another study found state-of-the-art blow dryers spread 1,300 more virus clumps than paper towels. Unfortunately, paper towels create waste, so perhaps not drying your hands at all might be the best thing to do.