Hand Drying Methods
Warm air dryers increase bacteria on hands – new research overturns hygiene perceptions
Warm air dryers can cause an average increase in the number of bacteria on people’s hands by up to 254% as well as potential contamination of the washroom environment.
These were the results of a 2008 study into hand drying carried out by scientists at the University of Westminster.
The study also showed that on average, paper towels reduce bacteria on the hands by up to 77%.
A second 2008 study into consumers’ attitudes to different hand drying systems highlights that given the choice, European consumers clearly prefer paper towels to either warm air or linen towel drying systems.
It is important to maintain good hand hygiene at all times, this is especially true when using a public washroom where there is a risk of contamination from other people. But it’s not always up to the user. A study of three different hand drying methods after hand washing, conducted at the School of Biosciences at the University of Westminster, shows that different drying solutions produce radically different results.
Warm air dryers cause an alarming increase in the amount of bacteria found on palms and finger pads. Three different types of hand drying solutions were tested: paper towels, regular warm air dryers and the new generation of “jet” air dryers.
Average bacteria count of bacteria on hands after washing and drying
Warm air dryers are proper “bacteria farms”
Regular warm air dryers performed by far the worst in the tests. They showed an average bacterial increase of 194% on the finger pads and 254% on the palms. The results suggest a radical increase in the amount of Staphylococcus aureus, a type of bacteria known to cause food poisoning, abscesses, boils and potentially penicillin-resistant infections. Drying time with a warm air dryer is also substantially longer than with the other systems studied (up to one minute compared to 10 seconds with a paper towel or linen towel roll) – damp hands pick up more bacteria than dry hands, acting like swabs when touching door handles and other washroom surfaces.
The study also tested the new type of “Jet” air dryer. “Jet” air dryers increase bacteria by an average of 42% on the finger pads and 15% on the palms. Air-based dryers do not only cause an increase of bacteria, they can also contaminate the washroom environment and other washroom users. This is caused by the high airspeeds of up to 400 mph that blow out of the unit. Tests showed that bacteria can spread as far as 2 metres from the “Jet” air dryer. Regular warm air dryers never spread bacteria further than 0.25 metres. Worryingly, separate research shows that over 80% of toilet seats have a lower mean bacteria count than the bottom of the “Jet” air dryer tested.
Paper the safest method
The comparative study confirmed that paper is the safest method of drying your hands after washing. In all tests, paper showed a reduction of bacteria. The average decrease was 76% on the finger pads and 77% on the palms. Also, paper is not likely to contaminate the washroom environment or other users. Furthermore, the 2008 study into consumers’ attitudes showed that paper towels are the first choice of users, with 61% opting for this method above the other hand drying systems studied.
Linen towel rolls
Separate research shows that drying hands with linen towel roll systems can on average provide a small reduction in bacteria levels of 4%. However, this is users’ least preferred of all the hand drying systems studied with only 8% of those researched (in the 2008 Study conducted by Intermetra Business and Market research) selecting it as their preferred choice. There are also hygiene implications of linen towel rolls as users often cannot help touching the used section of the roll to reach the clean section. In terms of costs, this system carries high maintenance costs due to frequent checks and roll changes. An average linen roll has a small capacity of only 40 metres resulting in a lot of refilling.
Research findings summary
|Bacteria present after drying
|Drying time (average for 90% dryness)
|Users' preferred choice
|Reduced by 48% - 77%
|1st choice - 61%
|Linen Roll Towel
|Reduced by 4%
|3rd choice - 8%
|Traditional warm air dryer
|Increased by 104% - 254%
|Up to 1 minute
|2nd choice - 31%