A new research paper shows evidence that hand dryers generate invisible “bacterial highways” inside buildings. The study builds on other recent research about how these devices suck up and disperse contaminated air, suggesting that these germs go on a much longer airborne journey from Paula’s favorite bathroom near accounting to, say, the coffee machine in engineering’s open kitchen.
The role of multiple types of hand dryers and paper towels in spreading bacterium, spores, and viruses has been hotly disputed in recent years. The Mayo Clinic published a study in 2000 claiming that there was no significant difference between “hot air” hand dryers and paper towels. Other studies have debated whether high-power “jet air” dryers like those popularized by Dyson spread less or more germs than regular hot air dryers or towels: one 2016 study published in the Journal of Applied Microbiology reported that jet air dryers spread 1,300 times more pathogens than a paper towel and hot air dryers are 60 times more infectious than a paper towel. Meanwhile, Dyson disputed that study’s methodology, pointing at a Dyson-funded study in the same journal reporting that jet air dryers equipped with HEPA filters spread fewer airborne infectious diseases than regular hot air dryers.
Suffice to say, the science of hand-drying is still contested. The new experiment conducted by researchers at the University of Connecticut’s School of Medicine is focused on hot air hand dryers specifically, rather than jet air dryers, and confirms that HEPA filters can make a difference here as well–but they are far from a solution. To study their effects, the researchers distributed petri dishes across every bathroom inside a building. Left open for two minutes with the hand dryers off, the plates averaged less than one bacterial colony. But when they turned the hand dryers on for 30 seconds, a clean batch of petri dishes averaged 18 to 60 colonies of infectious bacteria per plate, as well as spores of potential pathogens.
What’s more significant in this study, however, is that they found spores of a bacteria that they only grow in a lab very far away from this particular building. This, they say, indicates that “spores could be dispersed throughout buildings and deposited on hands by hand dryers.” One potential solution is HEPA filters, but their study found that filtered machines still blow plenty of pathogens into the air. The filters reduced the number of average colonies by four, but that’s still quite a bit of microscopic grossness.
Maybe the only solution is lunar colony-style pressurized bathrooms with hermetic doors. But that may be overkill, according to microbiologist Jack Gilbert, a scientist studying bathroom germs at Argonne National Laboratory in Illinois. “The restroom isn’t that dangerous,” Gilbert said in 2014. “The organisms which can grow there have a very low probability of being able to cause an infection.” (Tell that to the residents at a Hong Kong building who were infected by SARS thanks to the bathroom fans pushing contaminated air from bathroom to bathroom.)
I really need a shower.