Effect Measure

Like a lot of people I am more inclined to believe research that is in accord with my prior beliefs. Put another (Bayesian) way, I don’t have to change my beliefs much on the basis of evidence. That means I don’t question the evidence rigorously. So with that warning, here’s a story I instinctively believe because it accords with my prior beliefs — and preferences. It has to do with washing your hands after using a public bathroom.

To be clear at the outset: I always wash my hands after using the bathroom. I’m not sure what the actual evidence for disease transmission is but I consider it an aesthetic matter and good etiquette. But I also hate the hot air hand dryers many public bath rooms have installed instead of providing towels. Yes, I know there’s a solid waste issue. But it takes longer and it doesn’t leave my hands feeling clean. Now a study of paper towels, warm air dryers and the unique Dyson Air Blade hand dryer, done at the University of Westminster and paid for by the European Tissue Symposium, has validated my prior preferences. Note that the European Tissue Symposium doesn’t refer to biological tissue researchers. These are makers of paper towels, so consider the source. With that out of the way, here’s what they found:

There were four parts to the study: Part A looked at the drying efficiency of hand drying method; Part B involved counting the number of different types of bacteria on the hands before and after drying; Part C studied the potential contamination of other users and the washroom environment; and Part D took a bacterial sampling of Dyson Airblade dryers in public washrooms.

Paper towels and the Dyson Airblade were found to be equally efficient at drying hands, each achieving 90% dryness in approximately 10sec. However, the warm air dryer was considerably less efficient, taking 47sec to achieve the same level of dryness.

Twenty subjects (10 male and 10 female) were used in Part B. Three different agar growth media (nutrient, cystine-lactose-electrolyte-deficient and mannitol salt agar) were used to count and identify the bacteria on the fingerpads and palms before and after washing and drying.

Paper towels were found to reduce the number of all types of bacteria on the fingerpads by up to 76% and on the palms by up to 77%. By comparison, the Dyson Airblade increased the numbers of most types of bacteria on the fingerpads by 42% and on the palms by 15%. However, after washing and drying hands under the warm air dryer, the total number of bacteria increased by 194% on the fingerpads and on the palms by 254%.

The Dyson Airblade performed less well than paper towels and the warm air dryer in Part C in which the hands of 10 subjects were artificially contaminated with yeast suspension. During use, open agar plates were placed at 0.25m intervals from the hand-drying device up to a maximum of 2m. Yeast colonies that grew on the plates were counted.

The Dyson Airblade dispersed potential contamination to other users and the washroom environment to a distance of at least two metres, whereas paper towels spread contamination 0.50m and the warm air dryer 0.25m.

Part D showed that the Dyson Airblade dryers in the public washroom sampled were contaminated with large numbers of bacteria, including potential pathogens such as E. coli, staphylococcus and pseudomonas aeruginosa, particularly the bottom of the hand drying chamber

According to Keith Redway, senior academic in the department of Biomedical Sciences at the University of Westminster: ?The results of all parts of this study suggest that the use of warm air dryers and jet air dryers should be carefully considered in locations where hygiene is of paramount importance, such as hospitals, clinics, kitchens and other food preparation areas, schools, nurseries and care homes.? (Clean Room Technology [UK])

The Dyson Airblade folks are unhappy, saying the University of Westminster’s methodology was faulty and noting that this was paid for by the paper towel industry. I’m not able to judge with the information at hand (so to speak). But I’d much rather have a paper towel than an air dryer. Sorry, Dyson.

Comments

  1. #1 Thom
    February 19, 2009

    Let me do some Dyson advocacy. First, just because bacteria/yeast are present doesn’t mean that they are at levels that could be dangerous. Depending on how good the agar plates are, a colony could mean the presence of a single bacterium.

    Second, I don’t know the study’s methodology exactly or the materials that make up a Dyson blow dryer, but aren’t you just a little suspicious that an air dryer is a hot bed of bacterial activity? What about a bunch of metal, plastic, and high heat says, “Wow, this is the next best thing to an agarose plate!”

    It just strikes me funny and makes me suspicious of the study.

  2. #2 revere
    February 19, 2009

    thom: I grant your first point, which is why I was diffident about the validity but honest about my reaction to it. I’m not sure I understand your second point. It would seem that would make an air dryer a bad choice, not a defense of one.

  3. #3 dm
    February 19, 2009

    That’s too bad about the Dyson driers. I encountered them for the first time recently and was surprised to prefer them to paper towels. They’re fast and effective. I’m not surprised that stiff accumulates in the bottom of the machine, since one lowers one’s hands into the drier.

  4. #4 Aaron Golas
    February 19, 2009

    What about a bunch of metal, plastic, and high heat says, “Wow, this is the next best thing to an agarose plate!”

    It might be interesting to see how hot the various components of the air dryer get during use. But even so, Pseudomonas I know for sure is a thermophile. Turning up the heat is a boon to many bacteria, unless it gets hot enough for long enough to cook ‘em through.

    Another thing to look at would be how thoroughly air dryers usually get cleaned on a regular basis. At the very least, I doubt that cleaning personnel are opening the casings to disinfect inside, which could make the machine a prime safe haven.

  5. #5 Jeorge
    February 19, 2009

    I’d worry more about the bacteria and other unmentionables on the door handle than whatever might be on the dryer. Even if you use the dryers to dry your hands, you should still use a paper towel to open the door out of the restroom. You can’t know for sure if anyone else has done their business and washed their hands. Better to be safe than sorry. If a bathroom does not have paper towels, I use a wad of toilet paper and toss it in the trash on the way out. Anything else is just unsafe.

  6. #6 Adrian Simmons
    February 19, 2009

    It does sound one sided. Did they test the paper towel dispenser? Quite often one has to contact that to get some towels, and if you’re going to fish around in the bottom of the air blade and test the crud…and what about bins, so often you have to flip the lid of a bin to dispose of the towel.

    And is it just me that can never get their hands dry with a paper towel then? Must have big hands :(

  7. #7 biosplonk
    February 19, 2009

    Step 3: Dry hands on pants

    I’ve never liked electric hand dryers (though the new dyson ones are cool) so I agree with revere and find this study somewhat gratifying on a gut level. The results, if true, shouldn’t be hard to replicate if the dyson people really had a problem with the study being paid for by the tissue company. I find the results to be believable in terms of Part A certainly.

    Hospitals, perhaps the only neutral parties to conduct similar research, haven’t addressed the question directly but have instead concentrated on the amount of bacteria removed from hands by various drying methods. (A finding in the July 2000 Mayo Group Proceedings seemed to show that there was no difference between paper towels and electric hand drying in terms of amount of bacteria removed from hands) So the validity issues are likely to remain and the debate goes on.

    I still know which method gets my vote…

  8. #8 scouse
    February 19, 2009

    If there is one place germs are going to breed untouched by any cleaning fluids in public toilets it’s going to be the ‘Warm Air’ dryers. I say warm air specifically the air never gets too hot to pull your hands out of the way so they will never kill any germs!
    Paper towels must be the most hygienic because even with those cloth rolls you always touch a wet area to pull it down which has obviously just been used by someone else before you!

  9. #9 Boriswc1
    February 19, 2009

    I’m a bit confused by Thom’s comments also. If you didn’t have agar plates available and wanted to grow bacteria, then a supply of warm air combined with moisture is probably about the most effective breeding alternative available! So this report isn’t really surprising at all.

  10. #10 Mark P
    February 19, 2009

    I agree with Jeorge. It’s really hard to tear the blow dryer off the wall and open the door with it. That’s a reason to have paper towels and a trash can by the door, or doors that push to open from inside the restroom. Why aren’t they all that way?

  11. #11 DrA
    February 19, 2009

    I’ve often wondered about the energy efficiency of paper towels or reuseable cloth towels versus hot air dryers. Which uses the most energy? Which has the smaller carbon footprint? Which is the more ecological? Any ideas?

  12. #12 BW
    February 19, 2009

    In a restroom, once dropped something and when I picked it up, happened to see inside the hand blower. What a delightful, warm, fuzzy, damp place. I’d be a happy germ living there.

  13. #13 antipodean
    February 19, 2009

    But then again the Dyson airblade is the only hand dryer I’ve EVER used that actually dried my hands. They are amazing. But it is hard to not touch the sides or bottom of the well. Partly because the air is a lot stronger than you’re expecting.

    But then toilet doors still won’t open outward like they should so is it all just a waste of time anyway, as previous commenters have pointed out?

  14. #14 biosplonk
    February 19, 2009

    Perhaps the answer is not how you dry your hands but to put still more emphasis on hand-washing in general. Less germs to get blown around that way and the only true solution to the door/faucet issue. Not that its been all that effective thus far?

    Also, there seems to be as many arguments for which drying method is truly more energy efficient as there is for which are dirtiest. Apparently depends on how many variables you include in the math.

  15. #15 everett
    February 19, 2009

    Thanks to my brother-in-law, I subscribe to the pants dry, trees die philosophy. That is, why not [1] shake your hands a few times (and, [1a] if you’re like me and less or equally worried about contaminants on your trousers than those that you’d get from another method, wipe them lightly on your pants or maybe inside your pockets) and then [2] let them air dry. I feel like my favorite environmentalists would support such behavior — the one that has the least impact of any of these mentioned. Are we all such wicked witches that 15-45 seconds of wet hands turn us into a puddle?

  16. #16 Rory
    February 20, 2009


    Dyson vs wiping hands on pants.


    With conventional hand dryers, the ‘vs wiping hands on pants’ rages on, but not so with the dyson and the other new generation hand dryers. The centuries old tradition of drying your hands on your clothes has come to an end. It is surely about time that since the creation of man on the earth that we have developed a machine that can dry our hands properly. It also has to be said that the high speed hand dryers that have been around for a while (longer than the mitsubishi jet towel – which was the first new generation hand dryer – before dyson) also do a pretty sterling job. If it doesnt dry your hands in under 15 seconds, then its not worth a shht, seriously.

    New Gen and High Speed all the way (i do like paper towels too though, it has to be said, not very green or cheap, but good – hand dryers vs hand towels).

  17. #17 mara
    February 20, 2009

    Ho Ho what a joke! I observe that most people only wash their hands in restrooms if they know that they are being observed. And then it’s a 3 second cold water dribble.Oddly enough, most people believe that their own germs are harmless; it’s just the other guys’ germs that are filthy. If you do not agree with this comment, I suggest you have not been paying attention at ground level.

  18. #18 g336
    February 20, 2009

    First let’s start with the entire design of a public restroom. There is minimal visual privacy, and zero acoustical and olfactory privacy. (Warning, explicit language ahead…)

    You go into the cubicle and make a noisy stinky poo, and then you want to escape as quickly as possible to avoid embarrassment when the person who was sitting mere inches away from you as you did the deed, emerges to see the face of the person (yourself) who stunk him out. Worse yet at the office when it might be someone you know. Is it any wonder you only wash your hands for a few seconds? Or someone else is in another cubicle makes a loud stench and you want to escape from their noises & smells, so a quick cursory wash it is, and a hand on the dirty doorknob, and off you go to carry some fresh e coli as a condiment for your lunch.

    Improving the visual, auditory, and olfactory privacy of public bathrooms would put an end to the “gotta’ get outta’ here” syndrome. Case closed.

    As for the Dyson Dryers, the design flaws are as follows (having just looked at the pics on the webpage):

    The gap between the hands and the surfaces is too narrow, leading to the risk of contact with the surfaces particularly when the air turns on. A wider gap will solve this, but I’ll give Dyson a pass for not having thought of it.

    The concave surface at the bottom of the unit collects drippings from water running off hands as they are inserted. Then that surface gets nicely warm with all the warm air passing through the duct just under it. Perfect growing medium for little buggies dripped off the hands of those who only wash for a few seconds. Dyson doesn’t get a pass for this one, it should have been anticipated in the design in some way, for example by having the user insert their hands horizontally from the front, and mounting the infra-red sensors to the sides, and not having a closure at the bottom.

    The dispersal of buggies into the air for two meters is a direct consequence of a strong air blast. This would be an intrinsic problem of the design, between the lovely growing medium at the bottom of the area where you insert your hands, and the velocity of the air flow. An open bottom design as per above would help somewhat, and a suction intake under the hands would be splendid. Though, that suction intake would have to pass the air through a sanitizer of some kind, or out of the room through an outdoor vent, else the air would recirculate, germs and all, into the room.

    I could design a viable, sanitary, air dryer for hands, with a relatively small amount of capital to get to the prototype stage where the design could be evaluated independently. If interested, leave your address in spam-proof format…

  19. #19 scouse
    February 20, 2009

    Very interesting insight into behaviuor in the bathroom…

    I think that you might be better off spending your time designing a paper towel dispenser becasue that is obviously the way of the future. Also if everyone used paper towels after using the bathroom then at least the germs on the door handle would be dramatically reduced.

    With regards to which way is more eco friendly it must depend on whether or not the paper towels used are from a sustainable source or have any recycled paper in the mix or not.

  20. #20 Alexandra Lynch
    February 21, 2009

    I prefer paper towels, myself, because I have Raynaud’s phenomenon in my hands. It’s a delightful little peripheral vascular quirk where your fingertips lose blood flow if they think they are cold. One of the ways I can bring this on in the summertime is to wash my hands at the sink, use an air dryer to knock the larger water drops off, and exit back into an enthusiastically air conditioned room with damp hands. Paper towels are better, I can use two or three, dry my hands thoroughly, open the door, and I don’t see why they can’t compost the damn things or recycle them.

  21. #21 peggy
    February 22, 2009

    Learned this in nursing school:

    l. Dispense paper towels, but don’t tear off.
    2. Wash hands, but don’t turn off water.
    3. Tear off towel, dry hands.
    4. Using towel still in your hand, turn off faucet.
    5. Use towel, still in your hand, to open door. Toss on
    way out.

  22. #22 g336
    February 24, 2009

    Peggy’s right on target there.

    Use your elbow to operate the dispenser lever on the side of the paper towel dispenser, and let the paper towel hang down from the bottom of the dispenser.

    Then wash hands, etc…

    And/or, if someone else grabs the paper towel you had waiting for you, no worry, just use your elbow to operate the lever again.

    Now here’s a wild idea for you:

    Forget about hand-operated stuff in public WCs. Make it all foot-operated. This would not be difficult. For the towel dispenser, a foot pedal on the ground with a simple mechanical link to the dispenser lever.

    BTW, switching to all-foot operation of toilets, cubicle doors, and WC doors was first proposed in the journal _Public Cleansing & Salvage_ in the UK about 1965 or so. This is a tech journal of the Institute of Public Cleansing, more recently re-named the Institute of Wastes Management.

  23. #23 Hank Roberts
    February 25, 2009

    This reminds me of reading years ago — before the Web certainly, maybe before newsgroups — a study that concluded that hot air drying basically blew bacteria off leaving a measurable amount of bacteria normally found on the skin floating in the air in the bathroom for a while. Maybe they just set out agar plates.

    Conclusion was that wiping, not washing, is what removes most of the bacteria — the soap and water and rubbing removes some and just makes the rest let go of their hold on your skin.

    Then the paper towel takes them off effectively.

    Made sense to me. I’ve followed that routine since. And always, always, take a paper towel to use for the doorknob and fold it dirty-side-in afterward.

    Then if I forget and blow my nose or wipe my eyes with it later, only the strongest bugs that burrowed all the way through the paper will …. oh, wait ….

  24. #24 Boriswc1
    March 5, 2009

    I never realised G336 went through so much anguish when he went to a public loo!But good point. One massive disadvantage of the Dyson Airblad that no one has mentioned is that small kids can’t use it as hands have to be inserted from the top unlike other dryers – but again paper towels are better than all air dryers for kids.Particularly impotant as they have a habit of sticking their fingers in their mouths non stop. I don’t know how anyone who has ever been in a busy washroom in summer with the noise,heat and smell generated by 4 or 5 warm air dryers blasting away non-stop can ever think of them as anything but totally un-hygienic

  25. #25 Russell
    August 28, 2009

    So much for the notion that these blogs were populated by biologists who sleep in the field and laugh at the squeamishness of urban man. I’ve long said that most of the stories about public restrooms spreading disease were myth. Given the mysophobia here, they’re clearly a public health hazard!

    Or not.

    Yet no one has mentioned the obvious reason that paper towels are better than air blowers: they can be used to dry your face after washing it, to clean your spectacles, to wipe dirt off your shoes, to dab spilled wine off your shirt, to staunch the blood from a scratch, and for myriad other common self-care tasks to which air blowers are useless.

  26. #26 Mike
    August 28, 2009

    I’ll second Russell’s comment. About a year ago I fell off my bike and went chin-first into the pavement at 5:30 in the morning, leaving me with a gigantic, gaping wound that was dripping blood rather quickly. The first bathroom I went into had no paper towels, and I was not happy. (Fortunately the one two floors up did.)

  27. #27 Clare
    August 28, 2009

    As a resident of the US and former resident of/regular visitor to the UK, I’ve noticed for several years that paper towels have virtually disappeared from British restrooms/toilets. (To date, that’s also the only place I’ve come across those snazzy jet driers). So what other national or regional patterns of “restroom drying technologies” exist? Where, for example, can one still find those old cloth towels on a roll that you had to pull down to get a clean spot (they got stuck a lot as I recall – and did anyone ever look at their performance in terms of removing or replenishing germs on hands?) Or paper towels on a spindle that you have to wind, like an old clock, from the side of the dispenser (so much for the elbow trick)?

  28. #28 Katherine
    August 30, 2009

    Seems like a lot of people blow-dry their bottoms after using a public toilet, as they seem to not have encountered the toilet paper: “Yet no one has mentioned the obvious reason that paper towels are better than air blowers: they can be used to dry your face after washing it, to clean your spectacles, to wipe dirt off your shoes, to dab spilled wine off your shirt, to staunch the blood from a scratch, and for myriad other common self-care tasks to which air blowers are useless.”

    Public toilets are improving somewhat, I’ve encountered several with no-touch sensors instead of taps, no-touch sensors on the paper towel dispensors, and no external doors on the bathroom itself (instead having several turns so that no mens can look into the women’s or vice versa).

  29. #29 Michelle
    August 31, 2009

    My husband’s employer has completely hands-free operating bathrooms. Everything has a sensor, even the door. You wave your hand in front of a panel, the door opens. They’re deathly afraid of work-transmitted illness.

  30. #30 g336
    September 1, 2009

    If the science is convergent that paper removes more bacteria than air dryers, then we should be using paper towels. Use them with as much recycled content as possible, but use them no less.
    .
    We don’t object to “wasting” the paper we use to wipe our poopy bottoms, do we?
    .
    The place to save paper is not by cutting back essential uses that are related to public health or otherwise non-substitutable. The place to save paper is by outlawing all forms of junk mail including catalog updates that come out more than twice a year at most.
    .
    By analogy, going back to horse-drawn fire engines isn’t the way to save petroleum fuels; upgrading the efficiency of the passenger fleet and replacing car trips with public transport is.
    .
    As for Michelle’s husband’s employer’s computerized bathrooms, that’s unnecessary and it’s bad design because the sensors & digital circuits are the first things to break down and render the fixtures inoperative. Everything can be operated by foot pedals, that can also be designed to be operable by pressure from the wheel of a wheelchair. All strictly mechanical, no electricity needed, and nothing to break down. Every hand-operated device can have a plain metal rod from the handle to a tread plate on the ground; problem solved. For the sink, use hospital type sinks with foot pedals that operate the water valves.
    .
    This stuff is easy. All it takes is a bit of thought.

  31. #31 Lura
    January 4, 2010

    Fascinating conversation! An aspect I haven’t seen discussed here yet: the air dryers must, of neccesity, suck in air from the surrounding air of the bathroom, then blow it in concentrated form on your hands. That seems like an additional potential for contaminate to me.

  32. #32 Hand Dryers Manufacturers
    February 3, 2010

    Nice

    Hand-drying machine, clean – and based on expert advice. Some researchers have found that the hot air drying, to kill micro-organisms to speed up. Hand dryers in the hands of cracks, and even paper towels to dry skin may occur.

    Thanks for sharing this information.

  33. #33 Claire Roberts
    February 22, 2011

    I much prefer using hand dryers in public bathrooms. There’s so many new and different one about now like the Mitsubishi one called the jet towel. The new ones out dry your hands so quickly and are a really modern shape.
    The thing about hand dryers they are so much more energy efficient, less waste because think of the amount of paper being thrown away each time someone dries their hands! Plus it means somone will have to constantly empty the bins for the paper towels whereas hand dryers theres no waste.

    I like the look of the jet towel http://jettowel.mitsubishielectric.co.uk/ and they say that they have a reduction of 90% energy which is good!

  34. #34 tütüne son
    March 21, 2011

    As for Michelle’s husband’s employer’s computerized bathrooms, that’s unnecessary and it’s bad design because the sensors & digital circuits are the first things to break down and render the fixtures inoperative. Everything can be operated by foot pedals, that can also be designed to be operable by pressure from the wheel of a wheelchair. All strictly mechanical, no electricity needed, and nothing to break down. Every hand-operated device can have a plain metal rod from the handle to a tread plate on the ground; problem solved. For the sink, use hospital type sinks with

  35. #35 Hand dryers
    August 9, 2011

    Thanks that was a nice article … i will also follow your advice on washing my clothes while in the shower :) I am going to the laundry next week,hence I will follow those tips.

  36. #36 fire blanket
    September 20, 2011

    last i heard dyson said the study that proves hand dryers spread more germs was accurately paid for by paper towel manufacturers lmao

  37. #37 jjb
    October 5, 2011

    We recently performed this experiment with my college biology classes and came up with similar results for the dyson dryers – they increased bacteria on hands. To be fair, so did several other methods, which seems to come down to some contamination of the water. I would recommend clean pants over Dyson dryers based on our results. In trying to track down the source of contamination, I swabbed dyson dryers and discovered that its surfaces were dirtier than the floor. Not surpisingly, the air stream contained bacteria as well; while hot air dryers had a cleaner air stream in my samples.

  38. #38 Liz
    May 16, 2012

    I have recently read a lot about this subject, as we are trying to choose a better system for our office bathrooms to reduce the paper towel waste build up. My immediate reaction to the study results is that 10 seconds is not an adequete dry time. Dyson itself says repeatedly that their measurements are based off of a 12 second dry time minimum. Although 2 seconds may seem minimal, that reduced time takes away 17% of your drying potential. For bacterial growth on the warm, moist palms and fingers of a recently washed hand, this is very significant and could easily change the study results.

    With that said, I used a Dyson dryer recently and discovered that it took nearly 30 seconds for my hands to really feel dry! I was a little disappointed by the advertising in that respect.