This seems like an almost comically mundane topic, but it is one we face on a regular basis, and can be extremely important in certain environments. Which method of drying hands is superior – hot air dryers, paper towels, or the newer jet air blades (which blow room temperature but fast air)?
I was reminded of this issue while traveling recently in the UK. Almost without exception, all public bathrooms I visited had hot air blowers, often with self-congratulatory signs indicating that these were the environmentally friendly option. Always the skeptic, I suspected that the issue was likely far more complicated than that, and it is.
First we need to define our question, specifically what criteria will we use to determine which method is superior. I found studies looking at several criteria: effectiveness of hand drying (including compliance), carbon footprint, cost, the degree to which bacteria and viruses are deposited on the hands during the drying process, and the degree to which bacteria and viruses are spread from the hands to the environment.
I also found that many studies were sponsored by either the paper towel industry, or the air blower industry, with entirely predictable results favoring their products or maligning their competitors.
Another layer of complexity is the assumptions made during the comparison. Not all air blowers are created equal, and some are more efficient than others. Also, paper towels can vary in thickness, and be made from recycled paper or be recyclable or not. The method of paper distribution also affects the average amount consumed by each user. Further, the source of electricity affects calculations of the overall carbon footprint.
Cost and carbon footprint
The consideration of cost is less important from a medical perspective, but often is what drives decision-making. Here there is a clear and consistent answer – paper towels are more expensive than either hot air or jet air dryers. Estimates of course will vary according to the relevant variables I listed above, but on average paper towels cost 2-3 times as much per month as hot air blowers, and 10-20 times as much as an air blade. In one comparison, for example, paper towels in a heavy use environment would cost $1,460 per year, while an efficient air blade just $48 per year. Up front costs are higher, but they pay for themselves within a few months of heavy use.
For many companies, that is the end of the comparison. For those interested in minimizing carbon footprint, the answer is similar. Paper towel vs hot air blowers are about the same. They overlap in carbon footprint depending on the relevant variables, so no clear winner there.
However, air blades have a lower carbon footprint than both, when doing a thorough lifetime analysis. Air blades have about one-third the carbon emissions per drying than the other two methods.
Effectiveness and hygiene
Here is where comparisons get fairly complex, although there does seem to be a reasonably clear answer. Unfortunately, the answer is completely flipped from the cost and carbon footprint comparison – with paper towels being the clear winner.
A 2012 systematic review found that paper towels dry hands more quickly and more thoroughly than the air dryers available at the time. They concluded:
This review found little agreement regarding the relative effectiveness of electric air dryers. However, most studies suggest that paper towels can dry hands efficiently, remove bacteria effectively, and cause less contamination of the washroom environment. From a hygiene viewpoint, paper towels are superior to electric air dryers. Paper towels should be recommended in locations where hygiene is paramount, such as hospitals and clinics.
Also, air dryers that are used in many washrooms allow for only one user at a time and each person could take up to one minute to dry their hands. This is not convenient and often leads to avoidance or incomplete drying. In several studies, on average people spent just 22.5 seconds drying hands, and 41% wiped their hands unhygienically on clothes.
You might consider this an intention to treat analysis – if people aren’t compliant, it doesn’t matter how effective the intervention is. The authors of the review also point out that wet hands spread bacteria much more efficiently than dry hands, so just having more complete dryness is a significant advantage.
So here the bottom line appears to be that paper towels dry hands more quickly and effectively, and people use them more. With air dryers, people are more likely to incompletely dry their hands, or not dry them at all.
Air jet manufacturers would argue that their newer products are faster, solving the problem, but that remains to be seen in careful studies. The question, however, is a bit of a moving target as technology advances.
Recent attention has been paid to a number of studies looking at the spread of bacteria onto or from the hands during the drying process. Here the clear winner is also paper towels. A 2014 study found:
Jet air and warm air dryers result in increased bacterial aerosolization when drying hands. These results suggest that air dryers may be unsuitable for use in healthcare settings, as they may facilitate microbial cross-contamination via airborne dissemination to the environment or bathroom visitors.
A lot of attention was focused on a 2015 study that found that jet dryers spread 1,300 times more bacteria than paper towels. This study was criticized (mainly by Dyson, the maker of jet dryers) for being contrived – it used gloved subjects and exposed them to high amounts of bacterial contamination. It was more of a proof-of-concept study than real world study.
Regardless, there is a nice consensus of research that hot air blowers spread more bacteria and viruses from and onto user’s hands than paper towels, and jet dryers even more. As the authors note, this “suggests” that air dryers are less hygienic, but I could not find any studies looking at actual infection rates.
Given all of this, what is the best current decision regarding hand drying method in public spaces? The answer is – it depends. It depends upon your priorities.
If your major goal is minimizing carbon footprint or personal cost, than air jets are the way to go. If you want to maximize customer service, than it seems that most people prefer paper towels, given that they use them more and avoid or minimize their use of air dryers in high percentages. You can also provide both options and let patrons decide, depending on their preferences and current needs.
If, however, your primary goal is hygiene, which is the case in hospitals and other healthcare settings, then paper towels are the current clear winner. They dry hands faster, more completely, and minimize the spread of bacteria to the environment and cross contamination. Since hospitals are notoriously loaded with resistant infectious bacteria, this is clearly an important goal.
There are other considerations, however. Focusing on drying method ignores the issue of how hands are cleaned in the first place. There is clear evidence that washing hands thoroughly with soap is critical to good hygiene. If soap is used, then there is essentially no significant bacteria left to spread to the environment.
Further, hospitals generally use sanitizer, which contains alcohol and is self drying. The CDC recommends either washing with soap, or using a sanitizer with at least 60% alcohol to minimize bacteria. Some studies show that high alcohol content hand sanitizers are superior to hand washing for reducing bacteria, in fact. (Although hand washing is better for removing dirt.)
So wash your hands, use soap or sanitizer, and use whatever method is available to dry them effectively. Don’t let your hands drip dry, and don’t dry them on your clothes.