They do a terrific job of taking bacteria from your hands and spreading it all over the walls and floors.
Which is better -- disposable hand towels or the electric hand dryer? The totally unbiased European Tissue Paper Association funded a study a few years ago concluding "that single-use paper towels spread the lowest number of viruses of all the hand-drying methods." The equally impartial Dyson Corporation determined that its dryers, with their HEPA filters, did a better job. Yet another study found that electric dryers were effective at moving faecal bacteria from toilet to hands.
Now a new study published in the Journal of Hospital Infection looked at Environmental contamination by bacteria in hospital washrooms according to hand-drying method: a multi-centre study.The researchers, led by Mark Wilcox, Professor of Medical Microbiology at the University of Leeds, measured levels of contamination every day over twelve weeks in three hospitals in the UK, France and Italy, alternating between jet dryers and paper. Professor Wilcox is quoted in a Leeds University press release:
The problem starts because some people do not wash their hands properly. When people use a jet-air dryer, the microbes get blown off and spread around the toilet room. In effect, the dryer creates an aerosol that contaminates the toilet room, including the dryer itself and potentially the sinks, floor and other surfaces, depending on the dryer design and where it is sited. If people touch those surfaces, they risk becoming contaminated by bacteria or viruses.
Most of the contamination was on surface rather than in the air, so levels of bacteria change depending on how often the washrooms are cleaned. The UK and French washrooms were five times as filthy as the Italian ones; perhaps Italians wash their hands better before they dry them. People also often shake their hands before they dry them with a jet air dryer to speed the process; they may be spreading the bacteria that way. But even with all the variables, it was always worse with jet air dryers. Professor Wilcox:
“We found multiple examples of greater bacterial contamination on surfaces, including by faecal and antibiotic-resistant bacteria, when jet-air dryers rather than paper towels were in use. Choice of hand drying method affects how likely microbes can spread, and so possibly the risk of infection.”
Because the infection risk in hospitals is so great, French doctor Frédéric Barbut concluded: "These results confirm previous laboratory-based findings and support the recent French guidelines regarding hand hygiene, which discourage using jet-air dryers in clinical wards."
Another lesson from the study is that people should really wash their hands well before they hit the dryer, so that they are not contributing to the problem; whether paper or air, the dryer is supposed to be dealing with water, not bacteria.