I almost never use bathroom hand dryers, though I always wash my hands scrupulously (one reason, I think, that I didn’t get colds or the flu this year). But the reason has been time, not sanitation: it takes a long time for those things to dry your mitts, and I don’t like to linger in public bathrooms. Instead, if there are no paper towels, I will shake my hands off and let them air dry.
But now there’s an even better reason to avoid public hand dryers—both the hot-air dryers with nozzles and the jet dryers, shown respectively below:
That reason is bacteria. According to articles in BoingBoing, Ars Technica, and other places, based on a new scientific paper, these dryers spray potentially dangerous bacteria and viruses onto your hands—bacteria you wouldn’t get if you used paper towels or used the Coyne air-drying method.
Why? Because the hot air these things blow onto your wet hands has to come from somewhere, and it comes from the bathroom, where bacteria are floating around in the air, often expelled there by flushing the toilet. The dryers rapidly push a hot cocktail of bacteria and their spores (which can survive high temperatures) onto your hands, which you can then transfer to your body by touching your mouth, eyes, or nose. These bacteria can include, as the studies below suggest, Staphylococcus aureus, E. coli, Bacillus subtilis, and Clostridium difficile, as well as dangerous viruses. (Flu is, after all, caused by a virus.) It’s much worse than waving your hands around in the air, as a huge volume of air gets applied to your hands with the dryers.
Although we’ve known for three years that the dryers can disperse microbes from your hands to the bathroom at large, the news media are touting this new paper about how the devices themselves deposit microbes on your hands. You can access the paper by clicking on the screenshots. I’ve added the abstract in so you can see the extra bacteria deposited by dryers on a sterile plate (read: your hands after washing) compared to the air in the bathroom as a whole or bathroom air moved by a small fan. You can get the paper (free pdf if you have the legal Unpaywall app), by clicking on the screenshot. It’s in in Applied and Environmental Microbiology, a good journal:
Remember that these data were collected in bathrooms attached to “research facilities” (science buildings), but the relative enrichment of bacteria will certainly obtain in public bathrooms as well, though perhaps not the same numbers below.
Note the comparison:
Hand dryer (nozzle) for 30 seconds: 18-60 bacterial colonies per plate
Bathroom air (hand dryers off): less than one colony per plate
Plate blown by small fan in bathroom for 20 min: 12-15 colonies per plate
Hand dryers retrofitted with HEPA filters: about 11-16 colonies per plate
Even the Coyne method puts far fewer bacteria on your hands than a dryer with a HEPA filter!
As Ars Technica notes:
Indeed, in the wake of the blustery study—which took place in research facility bathrooms around UConn—”paper towel dispensers have recently been added to all 36 bathrooms in basic science research areas in the UConn School of Medicine surveyed in the current study,” the authors note.
The research findings largely square with other data [JAC: see below] showing that hot-air dryers and jet dryers can launch and disperse germs from hands into the air and onto surfaces—essentially setting off a very dirty bathroom bomb. But the new study clearly demonstrates that the less powerful hot-air dryers can also bathe hands with germs already swirling in the wash room.
I prefer to use paper towels: after all, who wants wet hands? The paper shown below, three years old, compares how the devices launch viruses into the air when your hands are already contaminated with viruses. That’s relevant because you could be making other people sick by using hot-air dryers, but not so much by using paper towels. And in bathrooms where other people are using hot-air dryers, you’re more likely to get hit by those microbes:
Here they used viruses instead of bacteria as an index of contamination, and did the measurements at different heights as well as different distances from the hand dryers. Here’s the relevant table. Look at the increased contamination of jet dryers compared to nozzle dryers, and how much less contamination of the atmosphere there is with paper towels.
The lesson: NEVER USE HOT-AIR HAND DRYERS IN PUBLIC BATHROOMS, and if other people are using them, stay away! Either use paper towels or the Coyne method of shaking and air-drying. I surely will never use another hot-air dryer again. Also, as all experts say—and I follow their advice—wash your hands thoroughly: twice as long as it takes you to sing the first verse of “Happy Birthday”, which I always run through in my head while washing.
Now I know that paper towels may be ecologically wasteful (though I don’t know how that compares to the electricity consumed by dryers), but who wants to get sick?
Avoid the dryers. You will get fewer colds and flu, and you will thank me for it. Professor Ceiling Cat (Emeritus) says, “You’re welcome!”