Using a hand dryer after washing your hands “is so unhygienic that it might be better to not wash at all”, according to The Daily Telegraph. The newspaper said that the moisture left after only partially drying your hands with an electric dryer makes the spread of bacteria more likely.
The news comes from a laboratory study which compared different hand-drying techniques in 14 volunteers who washed their hands in standard ways. It suggested that ultra-rapid hand dryers and conventional warm-air hand dryers removed similar amounts of bacteria from the hands as long as the dryers were used for an adequate length of time. It also suggested that rubbing your hands together while drying them may release more bacteria from the surface of the skin after washing. These results do not mean that using hand dryers is “unhygienic”, or that not washing your hands is better.
Effective hand washing is very important for reducing the transfer of bacterial and viral infections, so studies identifying the best hand hygiene methods are useful. Larger studies, and studies under normal hand-washing conditions, would be helpful to confirm the findings of this study. While the Telegraph seems to imply that avoiding hand washing may be a better idea, this is unlikely to be the case, and the best option is likely to be simply washing and drying your hands thoroughly.
Where did the story come from?
The study was carried out by researchers from the University of Bradford and the Microbiology Department of Dyson Limited. The study was also funded by Dyson Limited, the company that manufactures the ultra-rapid hand dryer tested in the study. It was published in the peer-reviewed Journal of Applied Microbiology.
This research was reported by the Daily Express and The Daily Telegraph. The Express suggests that “the safest options are paper towels or modern dryers that rapidly strip off moisture”, but the study suggests conventional warm-air dryers can perform as well as these methods if the hands are dried for the full amount of time that the airflow continues. The Telegraph said that using a hand dryer after washing your hands “is so unhygienic that it might be better to not wash at all”. This statement is not supported by this study, which did not assess the amount of bacteria on the hands without any hand washing.
What kind of research was this?
This laboratory study in human volunteers compared a conventional warm-air hand dryer with the Dyson Airblade, a newer ultra-rapid hand dryer manufactured by the company that funded the study. It was specifically interested in whether the dryers differed in how much bacteria they left on the hands, which could be transferred to other surfaces. The researchers were also interested in whether rubbing hands during drying affected the amount of bacteria left on the hands that could be transferred.
The researchers reported that although certain aspects of hand washing (such as types of antibacterial handwash used or hand-washing techniques) have been extensively studied, less research has looked at the contribution of hand drying to the effectiveness of hand washing.
The study used standardised laboratory conditions, and each volunteer used each of the drying methods, with the different methods tested in a random order. These were appropriate methods for testing the effects of the different hand dryers. The effects of the dryers in real-life situations, where conditions are not as controlled, may differ to some extent.
What did the research involve?
Two types of warm-air hand dryer were studied in this research, one operated with a push button and one automatic, as these are typical of hand dryers in common use. These dryers blow warm air downwards to dry the hands, which are also rubbed under the airstream. The manual dryer stays on for 30 seconds and the automatic dryer for 35 seconds.
The study compared the two warm-air hand dryers to an ultra-rapid dryer. The researchers say the ultra-rapid dryer uses two high-pressure “knives” of filtered room-temperature air to blow water off the hands, which are held apart and drawn through the airstream. The manufacturer’s recommended drying time for this dryer is 10 seconds. New dryers were used for this test to avoid any microbial contamination in a used dryer being transferred to the hands.
The researchers recruited 14 adult volunteers to take part in their two-part study. In the first part, volunteers handled fresh raw chicken and then washed their hands in a standard way using an unmedicated liquid soap. They then dried their hands in a variety of ways with conventional warm-air hand dryers, the newer ultra-rapid hand dryer or by allowing the hands to air-dry naturally.
The conventional driers were used either for 10 seconds (the same time as the ultra-rapid drier) or for their recommended length of drying time (30 or 35 seconds, the full length of time the airflow remained on after a single activation). Each volunteer used each drying method on a separate occasion, and the order in which they used the different methods was randomly assigned. After drying, volunteers pressed their fingertips onto sterile foil, and tests were carried out to assess the number of bacteria transferred.
The second part of the study aimed to see whether hand rubbing affected the results of hand washing and drying. In contrast to the first part of the study, it did not use deliberate contamination of the hands with raw meat, and soap was not used during hand washing as the researchers thought it might hide the effects of hand rubbing. This part of the study compared the two conventional warm-air hand dryers (with and without hand rubbing), the newer ultra-rapid hand dryer, and drying the hands with paper towels. All drying methods were used for 15 seconds. The amount of bacteria on palms, middle of the fingers and fingertips before and after washing and drying was compared for the different washing methods.
People with sores or cuts on their hands were not eligible to participate, nor were people who were being treated for skin problems or who had recently used antibiotics or antibiotic creams, which are used to kill bacteria.
What were the basic results?
In the first part of the study, the researchers found that the average amount of bacteria transferred to the foil sheets after the ultra-rapid dryer was lower than after use of the conventional warm-air hand dryers used for 10 seconds or unassisted air drying for 10 seconds. There was no statistically significant difference in bacterial transfer after using the conventional dryers for 10 seconds and air drying hands for 10 seconds.
Using the conventional warm-air hand driers for their recommended amount of time (30-35 seconds) improved their performance, and the levels of bacteria transferred after drying in this way were not significantly different from after using the ultra-rapid dryer.
In the second part of the study, the researchers found that if people rubbed their hands while using the conventional hand driers for 15 seconds, fewer bacteria were removed than if they kept their hands still during drying. If the hands were kept still while using the conventional dryers, the amount of bacteria removed was similar to the amount removed using the ultra-rapid drier for all regions of the hand tested.
Using paper towels to dry the hands removed a similar amount of bacteria from the middle of the fingers as using the dryers, and removed more bacteria from the fingertips than the dryers, although it was not clear whether this difference was statistically significant.
How did the researchers interpret the results?
The researchers concluded that effective hand drying is important to reduce the transfer of remaining bacteria from the hands onto other surfaces after hand washing. They say that rubbing hands during warm-air hand drying removes the benefits of hand washing.
They also suggest that the ultra-rapid hand dryer, manufactured by the company that funded this study, was “superior” to the warm-air dryers. They say that its faster drying time means that people are more likely to dry their hands, and therefore reduces bacterial spread.
Overall, this study suggests that newer ultra-rapid air dryers and conventional warm-air hand dryers perform similarly if used for the recommended lengths of time. It also suggests that rubbing hands together while using a conventional warm-air dryer may reduce the effects of hand washing. There are a few points to note:
- New hand dryers were used in this study, and volunteers used standard methods of hand contamination, hand washing and drying. This is an appropriate way to compare the potential effects of different hand dryers. However, these conditions may not be representative of what happens when people wash and dry their hands in real-life settings.
- The ultra-rapid hand dryer was only better than the conventional warm-air hand dryers if the latter were used for shorter periods than intended by the manufacturers (10 seconds as opposed to 30-35 seconds). This suggests that, for maximum effect, the hands should be left under the drying airstream of warm-air dryers for the full length of drying time.
- It was unclear whether researchers were blinded to which hand-drying method the subjects used. Ideally, the researchers would not have known which drying method was used to provide each sample being tested for bacteria.
- Many bacteria are harmless. However, the type of bacteria found on the hands, and therefore whether they might be harmful, was not assessed in the study.
- The second part of the study, which assessed the effects of hand rubbing, only used the conventional driers for 15 seconds. Had they been used for the recommended 30-35 seconds, the results might have been different.
- The study was relatively small. For each drying method, there was variation between individuals in the amount of bacteria transferred after hand drying. Testing in larger groups of people would be helpful to confirm results.
- New hand dryers were used in this study, so any bacteria found on the hands after drying would have come from the hands themselves or contact with meat in the first part of the study, not the dryer.
This study does not suggest that you are better off not washing your hands than using a hand dryer. It did not compare the amount of bacteria on the hands without any washing and after washing and drying. Effective hand washing is very important to reduce the risk of passing on infectious agents, so studies looking at the best way to reduce bacterial transfer are useful.