Study shows that electric hand dryers do a great job of concentrating bacteria and spraying it all over your hands

hand dryers bathroom
CC BY 2.0 Ben Husmann

But paper towels are four times as bad for the environment. What's a treehugger to do?

Life Cycle Analyses have shown that electric hand dryers are far better for the environment at large than paper towels, but a study sponsored by the paper towel industry showed that (guess what?) electric dryers were also much better at spreading bacteria and viruses.

Now Cory Doctorow at BoingBoing points to a new study by researchers at the University of Connecticut that seems independent, and which finds that, as ars technica so delicately put it, hot-air dryers suck in nasty bathroom bacteria and shoot them at your hands.

The paywalled study, Deposition of Bacteria and Bacterial Spores by Bathroom Hot-Air Hand Dryers, describes how the researchers put Petri dishes of agar under hot air dryers. According to ars technica:

In the still bathrooms, the researchers caught an average of zero to one bacterial landings per plate. When they left the plates open for 18 hours, that average leapt to six colonies per plate. But in the line of fire from the blowers for 30 seconds, the plates collected averages from 18 to 60, with a range as high as 254 depending on the bathroom.

So basically, when people flush the toilet, fecal bacteria and viruses get airborne. As Cory Doctorow puts it, "they hover in a miasmic cloud; when the dryers switch on, they pull these particles in through their intake, heat them up, and spray them onto your moist hands and other moist, hospitable surfaces where their bacteria can thrive."

The researchers note that HEPA filters on the fans cut the bacteria count by three quarters, so the Jet fans like Dyson's are probably better. (Dyson claims that their filters remove 99.97% of bacteria- and virus-sized particles from the air intake before the air is blown onto hands.) However, the researchers also found that certain bacteria were not captured by the filter:

In a final test, the researchers did a cursory look at some of the other bacteria the dryers were blowing around. They found that with or without a HEPA filter, the blowers stirred up potential pathogens, including Staphylococcus aureus.

The findings should be a wake-up call to managers of research and clinical settings.

Indeed, they should be a wakeup call for everyone. It's too bad that those roller towels aren't around anymore; perhaps we should all carry our own little towel; at least then we would also have something to open the door to the bathroom, probably the dirtiest thing in the room.

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