Sunday, November 23, 2014

That electric hand dryer study was bogus: Here's why

Just about everyone I follow on Twitter commented and/or linked to an article about a study claiming that electric hand dryers spew bacteria all over people using restrooms.

The paper, which appeared online in The Journal of Hospital Infection, said that airborne germ counts near jet air dryers were 27 times higher than counts near paper towel dispensers, and counts near warm air dryers were 4.5 times higher. The authors also coated subjects hands with black paint and measured spatter patterns on surrounding walls and persons dressed in disposable coveralls. And a photo from the study shows the dispersal pattern from a warm air dryer.

So case closed—paper towels are better, right?

I'm not so sure. Instead of reading an article about the paper or just the abstract, I obtained a copy of the whole paper. I also found some comments about it from a spokesperson for a hand dryer manufacturer.

What are the flaws in the study?


From the paper's Methods section: "For each test, gloved hands [not bare hands] were first coated by immersion in a suspension of lactobacilli (107 cfu/mL) that were cultured from a proprietary yoghurt." FYI, 107 cfu/mL is a lot of bacteria—certainly more than most of us would get on our hands during an average trip to the restroom. It's the equivalent of putting your hands in liquid feces, except that lactobacilli are benign bugs.

After dipping the gloved hands in bacteria, they weren't washed. Stick gloved hands in bacteria, don't wash them, and then stick them in an electric dryer. No doubt there will be dispersal of bacteria around the room.

Also from the Methods section: "For [another] test, gloved hands were coated in a solution of black water-based paint." Water-based paint on gloves is not the same as water on bare hands. Have you ever seen water all over the walls next to a warm air dryer? I haven't.

The study was funded by the European Tissue Symposium (ETS). Although this sounds like some kind of scientific conference, it is actually a trade organization of companies that make paper towels. The senior author of the study, Dr. M.H. Wilcox, "has received honoraria from ETS for microbiological advice and travel expenses to attend an ETS meeting." He also co-authored a consensus statement sponsored by the ETS which happened to find that paper towels are the most hygienic way to try hands.

I have always preferred paper towels. I feel that my hands can be completely dried in far less time than when I use the electric dryers. The drying process helps to reduce bacterial counts on the hands. Some studies have shown that when using electric dryers, many people do not completely dry their hands because it takes too long. See the table below.


A 2012 review of hand drying methods from the Mayo Clinic Proceedings concluded that paper towels were better than electric dryers from a hygiene standpoint, and that paper towels should be used in hospitals. [Note: One of the authors of that study had been a consultant to a paper towel manufacturer.] That's why you don't see electric hand dryers in patient care areas of hospitals.

I also hate the noise generated by electric dryers and the faster they are, the noisier they are. You can see the decibel levels of several devices in the table above.

The paper towels vs. electric hand dryers debate has been going on for years not only about hygiene, but also about which method is better ecologically.

Although I don't believe a word of the much-tweeted European Tissue Symposium study, I still prefer paper towels.




17 comments:

Emily said...

For me, those electric hand dryers are too slow. Most of the time I try to finish the job by flapping my hands in the air on the way out. I've even seen some people just wiping them on their clothes.

Skeptical Scalpel said...

Emily, I agree. I was going to put that in the post, but it was already too long. One article I read said exactly that. People become impatient and walkout wiping their hands on their pants

Anonymous said...

A co-worker told me she'd read that shaking your hands over the sink 12 times after washing them removes enough water that you only need one paper towel to dry them. I tried it and discovered it's true. So a few seconds more at the sink can halve the ecological effect of paper towel use.

frankbill said...

Would seem that the button that you touch to start the dryer would have the most bacteria of any place. So just starting the dryer would be a health hazard.

If you use the ones that have the sensor then more likely to touch the wall trying to get hands in right place to start.

Sometimes washing hands in sink with sensor can be more of health hazard then using paper towel or hand dryer. Don't know how many times I have touched the sink trying to get the water to run. Because of this don't always wash hands as good as I like.

Skeptical Scalpel said...

Anon, I had not heard that one before. You may be right.

Frank, Johns Hopkins Hospital has removed sensors for the faucets on its sinks. They found that there are more bacteria in the works of the sensors than you might acquire by touching the faucet. Pro tip: Use a paper towel to turn off the faucet when you finish washing your hands.

William Reichert said...

I use the paper towel to turn the knob on the bathroom door as I exit the bathroom. You should too.

Skeptical Scalpel said...

I usually do. You can't do that with an electric dryer. :-)

frankbill said...

My nephew told me about a new type of hand dryer that is suppose to stop the spread of bacteria. It has a place that you put your hands into that catches the water. Seems that the water puddles at the bottom of where you put your hands.

Julie said...

Here's the TED talk about how to use a paper towel: https://www.ted.com/talks/joe_smith_how_to_use_a_paper_towel

Changed my habits completely and I'm converting others as well.

Anonymous said...

if you want to waste 4.5 min of your life to learn how to dry your hands with one paper towel... https://www.youtube.com/watch?v=2FMBSblpcrc

Skeptical Scalpel said...

I'll save the rest of you from trying both links. They are the same talk. Thank Julie and Anon for nearly simultaneously commenting the same thing.

PS: The talk could indeed have been cut to 30 seconds.

Anonymous said...

Seems like the first thing you touch after pooping would have the most bacteria ..the soap dispenser and faucet handles.

Skeptical Scalpel said...

Well, that's why you wash your hands. You can use a paper towel to turn off the water or you can do it with your elbow like we once did in the OR before automatic faucets existed.

Eliot W. Collins said...

I don't like hand dryers, especially when you have to wait in line to use the only one in the men's room. I like paper towels because I can hold one in my hand to avoid touching the door as I leave the men's room.

Skeptical Scalpel said...

Eliot, good points. More reasons to go with paper.

Anonymous said...

Most people I've seen leaving public restrooms don't actually bother to wash their hands.

Skeptical Scalpel said...

That is true. It doesn't matter what the drying situation is if you don't wash your hands. I just returned from Ireland where air dryers including a lot of high-speed ones are nearly universal. It is hard to get completely dry when using one.

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