Mythconceptions  "A lot of Hot Air"

 Dr. Karl S. Kruszelnicki

                                                       (The Age, Good Weekend June 4, 2005)

I have always had niggling doubts about those warm-air hand dryers used in public toilets. They became popular because they claimed to be the most hygienic method of hand drying. It seems, however, the opposite is true - they can actually increase the number of bacteria on your hands.

In general, most people are terrible at hand hygiene. One in five people do not wash their hands before preparing food or after going to the toilet. One in six quickly wave their hands under cold running water, white only one in 10 actually washes for the necessary 30 seconds. Of every five people who do not wash their hands, one will not dry them properly, leaving a nice moist environment for leftover germs to go forth and multiply.

Traditionally paper or cloth towels were used for hand drying, but in 1953, Dr. Paul E. Walker, of the Public Health Service Hospital in Seattle, Washington, looked at drying hands with warm air. His report found there was "a probably significant reduction of cross-contamination of the hands when a mechanical air dryer was used". (A "probably significant reduction" is, in fact, not significant.) And "the mechanical air-drying technique is less expensive than the towel-drying technique". (This might be why you see so many warm-air blowers today).

In 1998, Keith Redway and Brian Knights, of the Applied Ecology Research Group at the University of Westminster in London, wrote their paper Hand Drying; Studies of the Hygiene and Efficiency of Different Hand Drying Methods. They looked at warm-air dryers - not in a sterile laboratory, but in real-world public bathrooms.

They compared disposable paper towels, continuous-loop cotton towels and warm-air dryers, and found that people would spend about 20 to 25 seconds using the dryer (compared with eight to 12 seconds using the other methods). This was about half the time needed to get hands 95 per cent dry, so about 60 per cent of people walked out with wet hands, while 40 per cent dried their hands on their clothes or hair. (Indeed, when public toilets users were given a choice, 69 per cent used paper towels, 18 per cent air blowers, and 13 per cent wiped their hands on their clothing.)

The real surprise was the difference in the number of bacteria left on the fingertips after using each of these drying methods. Washing and drying with paper or continuous-loop cotton towels reduced the germ count by between 45 and 60 per cent. But washing and using warm-air dryer in a public toilet actually increased it by an average of 255 per cent.

On further investigation, the researchers found that the bacteria were already inside the air dryers, thanks to the warm, moist environment. Every air dryer had high bacterial counts on the air inlet and outlet surfaces. (These figures would be lower in a clean laboratory.) In most cases, our immune systems are resilient enough to keep these bacteria at bay. On the other (slightly germy) hand, about 600 Australians come down with food poisoning every hour.

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