Alright, this question comes up in food safety circles a lot. There are as many opinions as there are variations on hand drying, and while there are some interesting questions about acceptability of hand dryers with respect to GFSI schemes, I don’t often see a lot of science-driven discussion about the actual effects or pros/cons on food safety, so let’s get into it.

For the purposes of keeping this analysis brief (me after finishing this article: HAHAHAHAHA O_o), we’re going to assume that activating any of the hand drying products below is “hands-free” eliminating them as a source of contamination by touching a button, turning a crank, etc. (Michaels Et al. 2001 found that touch surfaces became reservoirs for multiple pathogens) Then we’ll take the operation of the device step by step to evaluate potential contamination/re-contamination of hands and end with overall impressions.

So, we’ve just used soap and either hot or cold water (it doesn’t matter) to lather up and scrub for 20 seconds, rinse clean and shake off your drips….

*puts on cape and wizard hat*

…you find yourself in a tile chamber, dimly lit by glowing gems inset into the walls. Your movements echo quietly and you can smell fresh water. Your hands are wet and dripping, but clean. Exits are North, South, East, and Dennis-er I mean West.

North – Paper Towels

Let’s start with the standard, shall we?

You take several steps to the north side of the room, before you approximately 5 feet up the wall a paper towel dispenser is attached. It watches you with a glowing red eye as you approach. A mostly-full waste bin stands next to it, filled with paper towels. Suddenly, a motor whines and 6 inches of white paper come shooting out at you! Make a dexterity check and roll for initiative.

Okay, let’s use the paper towel.

You wave and additional towel is dispensed, you pull it free and a new piece is dispensed. You grab another and vigorously rub your hands, you toss the now damp paper into the waste bin. Combat over.

There’s more going on here though.

First of all, we rolled high on handwashing, so we achieved a solid 3-log reduction. That doesn’t mean the organisms are gone however, as that would require us to have fewer than 1000 organisms on the surface (give or take a confidence interval). This means that the drips on our hands potentially contain additional organisms, some of which may be pathogens (arguably the only ones that matter for this assessment). So there are several sources of pathogens that we need to consider here:

Those remaining on our hands

Those on the paper towel

Those in the surrounding air

We’re working with ambient air, so unless you’re waiving around like you just don’t care or actively blowing on your hands (I don’t think I need to address that in this post, do I?), we can only do so much with that. There will be bacteria, and if there are aerosolized particles with pathogens they may be a concern. However that’s a bathroom sanitation issue, not a hand drying one.

As we begin to remove water from our hands with the towels, we’re in the tricky land of bacterial transfer. However, as I stated above, food safety really only cares about pathogens in this scenario, so what’s happening? Dyson makes the claim that “up 88% of unused paper towels contain bacteria.”

-_-

I am, in this particular case, unimpressed, and Dyson should be embarrassed. This is a common meaningless measurement to sell antimicrobial stuff. As it turns out, the only places that regularly don’t contain bacteria are surfaces above 140ºf, the insides of autoclaves, pure chemicals, and post-treatment sterile items/surfaces. If “contains” bacteria has food safety implications, then we’re going to have to figure out how to sterilize our skin, mouths, and colons.

Here’s where they’re not wrong. Paper towels are not regulated as food contact surfaces, indirect food additives, or really any other sort of hygienic standard. They’re regulated as paper and consumer products. To share a touch more meaningful data than Dyson, Gendron Et al. found general aerobic organisms at concentrations between 2-5 log/gram of paper towel. Fairly standard for a surface. They noted that recycled paper towels had higher counts, but while Clostridium spp. were found, there isn’t a generalized correlation between the presence of the most common foodborne pathogens and paper pulp like there would be for a food products (e.g. salmonella in eggs). If this was the case, the authors noted that the organisms readily transferred from the towels to gloved hands so this could be an issue…if there were actually pathogens there, which is unlikely.

So how about the pathogens remaining on the hands? Well, if they’re there, and we know things transfer back and forth between the paper towel and the hands, presumably we can assume that the paper towel does conduct some microbe removing action. Patrick Et. al. noted that “residual moisture” on the hands greatly increases bacterial touch/contact transfer between surfaces and hands, and getting things dry plays a large role in keeping hands from becoming recontaminated.

I’ve heard several colleagues note that hand drying mechanically with paper towels has the potential to “undo” bad handwashing practices as soils would be removed onto the paper towels even if they did the ‘ol “rinse and go”. We don’t have a good study on soil removal but this feels somewhat plausible as anyone who’s ever removed automotive grease with a towel can attest, and a couple authors (Coates Et al.) have noted that the differences between soaps tend to wash out (*bah dum pish*) when followed by hand drying with paper towels. However, this idea is less meaningful when we’re assuming the hands were properly washed and/or there weren’t a lot of soils to remove (as is often the case in food processing between repeated handwashing and glove use). Further, Yamamoto Et al. found that three sheets of paper towels didn’t meaningfully decrease bacteria on hands except on fingertips, a finding supported by additional comparisons made by Ansari Et. alo.

One more reason for discrepancies between hand drying studies is that the methodology varies so much between tests, and it’s also hard to predict what people will tend to do anyway. Warm water is encouraged in the code, not because it is more effective at removing pathogens, but because nice warm water encourages handwashing vs. an uncomfortable ice-cold rinse. Warm water can also be more effective at removing fatty residues (e.g. hamburger grease). Paper towels have the advantage of being extremely quick at drying hands. Redway and Fawdar found that paper towels did the job in 10 seconds, while some air dryers take upwards of 20 or more for the same moisture removal.

A final bit in our paper towel journey is it’s destination, the waste bin. As anyone who’s ever used a public restroom knows, somehow people seem to miss the bin. I know. Or it’s full, or they tear small scraps off the paper towels…it’s a mess. Does it meaningfully contribute to pathogen risk? I’d say very unlikely, after all, it’s all on the floor. However it is a PITA for restaurant owners and food manufacturers who want to keep those areas tidy.

Paper towel advantages

No forced air movement

Potentially will remove additional soils from bad handwashers

Not sterile, but less likely to contain pathogens from hands, and with equal transfer rates thus then would potentially reduce overall remaining pathogen load on hands

Fastest hand-drying time for time efficiency and encourage employees to not rub hands on clothing to dry

Have not been proven to be any worse that other drying methods in multiple studies

that other drying methods in multiple studies Low upfront cost

Paper towel disadvantages

No food safety standards for paper towel manufacturing

Expensive, requires constant maintenance/replacement

Waste bins could become source of contamination or filth

If you run out and don’t replace, your bathroom isn’t in compliance with the food code or 21 CFR 117

South – Clamshell/U-shaped Jet/Airblade type hand dryers

You take several steps to the south side of the room, before you resting on a pedestal is a large U-shaped appliance. An eldritch symbol is stamped on it’s surface. LED’s and shapely design suggest it has value, you reach forward and place your hands inside…

No reason to mince words here, the types of dryers I’m covering here are two common make/models: the Dyson Airblade “dB” Model and the Mitsubishi Jet Towel dryers. These dryers use opposing flat jets of air to “squeegee” water from the hands as they are raised and lowered into the dryer.

As we begin to lower our wet hands into the dryer, a loud motor kicks in and a rush of wind pushes the skin around, we can see the water flecking off our fingertips into the bottom of the dryer. The process is effective and we see hand drying times comparable to those we saw for paper towels (10 seconds). In general, the studies for hand drying efficacy have been varied, but the ability of high pressure Jet/Airblade dryers to actually remove bacteria via moisture and dry the hands ultimately ends up just about as good or indistinguishable from paper towels (Snelling Et al., Matthews and Newsom, Gustafson Et al.). While certain experimental parameters show better efficacy with paper towels, when hand dryers are given sufficient time to do their thing they tend to hold up well.

Of particular interest and surprise to me was that the action of rubbing hands together while using hand dryers actually makes them less effective (Snelling Et al. and Yamamoto Et. al.). This is crazy and the reasoning isn’t clear. Perhaps additional bacteria are freed from cracks and crevices on the hands during the rubbing action , or that instead of the water blowing off the hands, and taking bacteria with it, it evaporates from the skin leaving bacteria behind. This translates into a benefit of the clamshell/U design, in that the way you dip your hands in to allow the airstream to do its thing provdes no room or particular reason to try and rub hands together while in the machine.

Unfortunately, I have some FF&F experience with these dryers that gives me pause. Typically most people see a dryer, dry their hands, and move on. Food safety people see the matrix. Because of the “U” shape of the dryer, the water that is blown from the hands collects in the bottom of the basin. Generally, for infrequent use, this isn’t a huge deal because the small drops of water quickly evaporate. However during heavy use (such as in a restaurant, food manufacturer, or popular bathroom), this water adds up, collects in the dryer, and eventually flows down the side of the dryer onto the floor. As we said above, you only achieved a 3-log reduction with your superb hand wash…what happens when someone who does a “rinse and go” introduces pathogens or fecal material to that water, and it stays moist for days?

Keep an eye out for it, I took the following pictures at a high-use gas station bathroom in Central Oregon:

This means that right where people need to stand to dry their hands, you’ve created a dirty puddle that will make an excellent Listeria/Salmonella/environmental pathogen breeding ground that you force food service employees to walk through before going anywhere else. I’ve seen these puddles completely covered in fuzz or slime, and I’m certain they’re a potential harborage point for environmental pathogens. Clearly from the dryer above, you can see how extremely frequent cleaning would be necessary to prevent soil buildup in the moist areas, which will require regular maintenance (I would suggest daily cleaning of the dryer and mopping of the floor below if water tends to accumulate based on usage). The Mitsubishi Jet Towel dryer attempts to fix this problem by including a drain in the “trough” of the dryer and collecting the excess liquid in a reservoir. This would certainly seem to solve the problem of the pooling on the floor, but not that of a generally moist environment in the trough, and the need for same same amount of maintenance to empty the trough at whatever necessary frequency.

Because of this situation, the potential for hand dryers to disperse bacteria and virus’ from hands has also been examined heavily. Kimmitt and Redway made waves with their study on virus dispersal last year, which demonstrated that the high speed air in these dryers is more effective at aerosolizing and distributing norovirus surrogates (MS2) than paper towels or warm air dryers (and prompted some angry Dyson responses). This is an unsurprising result, if only because higher air pressures would clearly be better at dispersing bacteria or viruses contained within water droplets or free flowing in the air, and Dyson has powerful air pressure in their systems in general. These results match those found in 2011 by Redway Et al.

Finally, there’s the potential bacteria introduced to the hands by impaction. We discussed that for paper towels you’re only exposed to ambient air, meaning that organisms found in the air can only settle on the hands as long as they are exposed. However we know from gauging microbial quality of the air for various food safety and clean-room standards that “impaction” air samples can recover 2-10 times more organisms than samples allowing them to settle in ambient air (Salustiano Et al.). This means that if the dryer is pulling in unfiltered ambient air, it is going to ultimately hit your hands with more bacteria, at a higher transmission rate, than simply exposing them to ambient air would. The Dyson dryers fix this problem by using a HEPA filter on the intake, the Mitsubishi dryers do not include one. So points for Dyson (assuming that you would be introducing pathogens found in the bathroom, not harmless organisms).

Clamshell blade/Jet Dryer advantages

No need for waste bin or paper towel inventory

Discourages rubbing hands while drying, increasing effectiveness

Fast hand-drying time for time efficiency and encourage employees to not rub hands on clothing to dry

Generally superior to hot air dryers in comparison studies at bacteria removal

HEPA Filtration is available to reduce possibility of contamination from forced air

Provided it’s functional, always have drying capability for 21 CFR 117 and food code compliance

Clamshell blade/Jet Dryer disadvantages

Potential to collect moisture and encourage biofilm development on/beneath dryer

Potential to recontaminate hands with fouled surface inside dryer

Excess water on dryer/floor requires regular sanitation schedule

Expensive upfront cost

Potential for dispersal of pathogens from contaminated hands from poor/insufficient handwashing via high pressure

East – High pressure jet dryers

You take several steps to the east side of the room, attached to the wall is a large shrouded motor with openings beneath. The wall is stained with water deposits below the dryer. A sense of power emanates from the machine and all objects in the room almost appear to be edging away from it….

Examples here would be the newer models of Dyson Airblade V and Xlerator hand dryers. These dryers use high pressure air in jets or knives to blast water from the hands.

Not much to say here that wasn’t said above for the other jet dryers. They dry almost as quickly as paper towels and with similar efficacy. A major difference is the sanitation surrounding the area. You still need to deal with the potentially large amoutns of water that are being sprayed onto the floor beneath the dryer, however in this case you also have the potential for drywall/paint moisture damage over time. Many places recommend installing a waterproof barrier such as tile, plastic, or FRP on the wall directly below the dryer to act as a backsplash, preventing damage and allowing effective cleaning.

If you’re going to go with a jet dryer, these are my recommendation as I’d rather have extra water on the wall/floor than immediately adjacent to the hands and in the flow of the high pressure air. In this way, if hands introduce pathogens to the area, they will be contained to the wall and floor and not be dispersed as far nor so closely to the hopefully clean hands. A quick mop of the floor and wipe of the wall is also arguably easier for sanitation personnel than crawling around all sides of the clamshell dryers above to get all surfaces clean.

Unfortunately it is also habit to rub hands together with the additional space given to you, which we noted above reduces the efficacy of hand dryers. Dyson’s blades may play a role in discouraging this behavior, but I don’t have any data to back that up. HEPA filtration to reduce the amount of airborne bacteria impaction depends on manufacturer.

High pressure Jet Dryer advantages

No need for waste bin or paper towel inventory

Fast hand-drying time for time efficiency and encourage employees to not rub hands on clothing to dry

Generally superior to hot air dryers in comparison studies at bacteria removal

HEPA Filtration is available to reduce possibility of contamination from forced air

Provided it’s functional, always have drying capability for 21 CFR 117 and food code compliance

Excess moisture is on the floor and wall away from the clean hands

High pressure Jet Dryer disadvantages

Potential to distribute moisture and encourage biofilm development beneath dryer on wall/floor

Potential for water damage on drywall or painted surfaces below dryer

Excess water on wall/floor requires regular sanitation schedule

Potentially expensive upfront cost, though pricing is variable

Potential for dispersal of pathogens from contaminated hands from poor/insufficient handwashing via high pressure

Potentially encourages rubbing of hands, reducing efficacy of pathogen removal

West – Hot Air Hand Dryers

With a sinking feeling, you look to the west. Against the wall is a small stainless box with a spout. It looks relatively untouched and you feel that it has little value. Slowly you approach with low confidence, Dennis stands to the side, wiping his hands on his jeans as he heads towards the exit…

I did not save the best for last. Of all hand drying methods, he classic low pressure hot air dryers (basically a hair dryer pointed down) either required in excess of 30 seconds to successfully dry hands to the same level as paper towels, and/or ultimately performed much more poorly at removing organisms from contaminated hands. They also encourage rubbing hands together to speed up the process, which was shown to reduce the efficacy of all hand dryers.

In addition to their actual effectiveness, they don’t bode well for hand washing compliance. Todd Et al. noted, via several studies, that on average 41% of people wiped their hands on their clothes to dry them when they determined other drying methods were ineffective. Patrick Et al. through experimentation determined that that hot air dryers took 45 seconds to achieve the same level of dryness (residual moisture) as paper towels could in 10 seconds.

Go ahead, stop reading the article and wait for 45 seconds.

…

Did you make it? Would you rather leave and let your hands air dry or give a quick jeans wipe? Not only was that boring for you (when you want to get back to work/to lunch/whatever), but based on the observations of Strohbehn Et al. in retail foodservice operations, you could require hand washing anywhere from 7-29 times per hour based on when you SHOULD be washing hands per the food code. Even if it was on the low end of 10 times per hour, you would be stuck at the hand dryer for 7.5 minutes per hour or 12.5% of your working hours!

Not gonna happen.

In addition, we still have increased dispersal action over paper towels (though less than the jet dryers), hot air dryers are less likely to include HEPA filtration to prevent impaction of airborne microorganisms (though there could be some reduction due to the temperature of the coils? The Time/Temperature/Relative humidity of the interaction makes this extremely unlikely), and we still have the same problem of water droplets all over the wall and floor.

Can you tell I’m not a fan? Don’t install these.

Hot air blower dryer advantages

No need for waste bin or paper towel inventory

Provided it’s functional, always have drying capability for 21 CFR 117 and food code compliance

Most inexpensive dryer option

Hot air blower dryer disadvantages

Potential to distribute moisture and encourage biofilm development beneath dryer on wall/floor

Potential for water damage on drywall or painted surfaces below dryer

Excess water on wall/floor requires regular sanitation schedule

Potential for dispersal of pathogens from contaminated hands in immediate area

45 second drying time discourages hand washing, encourages re-contamination by clothing or windmilling arms

Least effective of all options per literature

Lack of filtration may introduce pathogens to hands via impaction

Encourages rubbing hands which reduces efficacy

Epilogue – The Adventure Continues

Having defeated all four puzzles of hand, you must now choose your path…choose wisely, as pathogens lurk around every corner….

Ultimately I agree with the conclusions of many of the healthcare-centered authors that looked at this issue, and agree that, in critical areas where handwashing compliance is key and bacteria dispersal is an issue, paper towels remain the best, most hygienic option. In the food facility, this means that handwashing stations that are located near product contact areas and high-risk/high-care areas should probably utilize paper towels.

However, this doesn’t mean we can’t take advantage of the newest dryer tech that is holding its own in terms of drying efficiency and pathogen removal. Plant locations such as inside bathrooms, maintenance shops, and main facility entrances aren’t necessarily going to be harmed by the dispersion issues the high-pressure options have, and a strong sanitation/custodial program to ensure the dryers themselves don’t pose a contamination risk via standing water further reduces that risk.

By selectively choosing hand dryer locations, you can use them where they eliminate a lot of paper towel waste, but don’t incentivize employees to skip or poorly wash hands when/where it matters most. Heck, if an employee decides that they want to bypass the plant entrance hand-wash in favor of using the sink in the room that has a paper towel dispenser, you can feel good about the fact that you have a food safety culture in which employees think about where they will wash their hands. And if an employee wipes their hands on their clothing in the bathroom with the old hot air dryer, at least when they re-wash on the line they’ll have a more hygienic option available before they handle food.

Think about the science, think about the incentives, then work on making things “same or better”.

Ding! You gained 1000 experience.

Some helpful literature cited in this article:

Huang, Cunrui, Wenjun Ma, and Susan Stack. “The hygienic efficacy of different hand-drying methods: a review of the evidence.” Mayo Clinic Proceedings. Vol. 87. No. 8. Elsevier, 2012.

Strohbehn, Catherine, et al. “Hand washing frequencies and procedures used in retail food services.” Journal of food protection 71.8 (2008): 1641-1650.

Jensen, Dane A., et al. “Quantifying the Effects of Water Temperature, Soap Volume, Lather Time, and Antimicrobial Soap as Variables in the Removal of Escherichia coli ATCC 11229 from Hands.” Journal of food protection 80.6 (2017): 1022-1031.

Gendron, Louis McCusky, et al. “Evaluation of bacterial contaminants found on unused paper towels and possible postcontamination after handwashing: A pilot study.” American journal of infection control 40.2 (2012): e5-e9.

Patrick, D. R., G. Findon, and T. E. Miller. “Residual moisture determines the level of touch-contact-associated bacterial transfer following hand washing.” Epidemiology & Infection119.3 (1997): 319-325.

Yamamoto, Yukiko, Kazuhiro Ugai, and Yasuko Takahashi. “Efficiency of Hand Drying for Removing Bacteria From Washed Hands Comparison of Paper Towel Drying With Warm Air Drying.” Infection Control & Hospital Epidemiology26.3 (2005): 316-320.

Ansari, Shamim A., et al. “Comparison of cloth, paper, and warm air drying in eliminating viruses and bacteria from washed hands.” American journal of infection control 19.5 (1991): 243-249.

Redway, Keith, and Shameem Fawdar. “A comparative study of three different hand drying methods: paper towel, warm air dryer, jet air dryer.” European Tissue Symposium. Vol. 1. 2008.

Snelling, Anna M., et al. “Comparative evaluation of the hygienic efficacy of an ultra‐rapid hand dryer vs conventional warm air hand dryers.” Journal of applied microbiology 110.1 (2011): 19-26.

Matthews, J. A., and S. W. B. Newsom. “Hot air electric hand driers compared with paper towels for potential spread of airborne bacteria.” Journal of Hospital Infection 9.1 (1987): 85-88.

Gustafson, Daniel R., et al. “Effects of 4 hand-drying methods for removing bacteria from washed hands: a randomized trial.” Mayo Clinic Proceedings. Vol. 75. No. 7. Elsevier, 2000.

Kimmitt, P. T., and K. F. Redway. “Evaluation of the potential for virus dispersal during hand drying: a comparison of three methods.” Journal of applied microbiology 120.2 (2016): 478-486.

Michaels, Barry, et al. “Water temperature as a factor in handwashing efficacy.” Food Service Technology 2.3 (2002): 139.

Coates, D., D. N. Hutchinson, and F. J. Bolton. “Survival of thermophilic campylobacters on fingertips and their elimination by washing and disinfection.” Epidemiology & Infection 99.2 (1987): 265-274.

Michaels, B., et al. “The significance of hand drying after handwashing.” Culinary Arts and Sciences III (2001): 294-301.

Salustiano, Valéria Costa, et al. “Microbiological air quality of processing areas in a dairy plant as evaluated by the sedimentation technique and a one-stage air sampler.” Brazilian Journal of Microbiology 34.3 (2003): 255-259.

Todd, Ewen CD, et al. “Outbreaks where food workers have been implicated in the spread of foodborne disease. Part 9. Washing and drying of hands to reduce microbial contamination.” Journal of food protection 73.10 (2010): 1937-1955.