Skip to navigation | Skip to content

'Hygienic' hand dryer hypothesis blows hot air

Many believe that those warm-air dryers in public toilets are there to improve public health. But Dr Karl sees other motives behind their installation.

Hand pulling paper towel from a dispenser

(Source: iStockphoto)

Last time, I talked about handwashing hygiene, when you're away from home and using public conveniences, which includes the act of actually drying your hands. This drying should not just remove water. It should also remove bacteria.

Now there are different ways of drying your hands: paper towels, continuous-loop cotton towels and warm-air dryers.

Researchers got a real surprise when they counted the bacteria left on the fingertips after using these drying methods.

Washing the hands, and then using paper towels or continuous-loop cotton towels reduced the bacterial count by about 45–60 per cent. But washing, and then using a warm-air dryer actually increased the bacterial count by an average of 255 per cent.

How could drying your hands increase the number of bacteria on your skin?

When they went looking further, the researchers found out how. The bacteria were already inside the warm-air dryers, thanks to the warm moist environment. Every single warm-air dryer they tested had high bacterial counts on the air inlet, while 97 per cent had them on the outlet nozzle surfaces as well.

These were the figures for warm-air blower in public toilets. Of course, if you choose to do your measurements in a clean laboratory, you'll find lower bacterial counts.

Just imagine warm air blowing over poorly washed moist bacteria-laden fingers in a grimy public toilet. It's an ideal way to spread bacteria and other germs through the air, in an aerosol of tiny droplets.

But in most cases it doesn't matter, because our immune systems are resilient enough to keep the numbers of these bacteria low. Furthermore, the overwhelming majority of these bugs are fairly harmless. They don't usually include the real nasties like salmonella, shigella, campylobacter, hepatitis A or B, the SARS coronavirus, or the virus that causes meningococcal disease.

Now one important reason that you want to dry your hands is to remove the bacteria that are floating in the thin layer of water. After all, if you just let your hands dry slowly in the air, the bacteria will still be sitting on your skin.

With a towel (paper or cloth) you can apply some decent mechanical friction to your hands. This is an important part of the hand-cleaning process.

A towel soaks up the water, and the bacteria end up in the bin. You can dry 90 per cent of the surface area of your hand within 10 seconds with a towel. If the towel is in one place in the washroom, and the bin is in another, you can dry 90 per cent of your hands while you walk from one place to the next, and then walk out.

This suits most people just fine. After all, most public toilets and washrooms are not the kind of place where you want to spend your spare time.

A warm-air dryer cannot dry your hands within 10 seconds. Part of the reason for this is that in most cases, the wind blast is so pathetically gutless.

On average, they take 50 seconds to dry 90 per cent of your hands. This is really inconvenient, especially when other people are queuing up behind you to dry their hands.

They also have the problem of spreading bacteria. But, as I said before, in the vast majority of cases, these bacteria are not really a health risk.

Jet-air dryers have come on the market in the last few years. They blast air at enormous speed (they claim over 600 kilometres per hour, which I find hard to believe) and with enormous noise.

If you can apply some mechanical friction, and rub your hands together, you can dry 90 per cent of your hands within 10 seconds. This is good.

On the other hand, because the air does move faster, the jet-air dryer can blow bacteria some two metres, rather than the half-metre-or-so of a gutless warm-air dryer. But then again, the overwhelming majority of these bacteria are not dangerous.

And if the jet-air dryer has a good intake filter, it will stop the bacteria that are already floating in the bathroom air from getting sucked in and blown around.

Probably the most important lesson to take from this is to get into the regular habit of washing and drying your hands. Drying your hands on your jeans or hair is better than not drying them at all.

And don't believe that warm-air dryers were installed to improve hygiene. They are purely a cost-cutting measure. Anything else they tell you is a lot of hot air.

Tags: health, vaccines-and-immunity

^ to top

Published 15 February 2011

© 2014 Karl S. Kruszelnicki Pty Ltd