Not drying your hands thoroughly after washing them could increase the spread of bacteria and rubbing your hands while using a conventional electric hand dryer could be a contributing factor. Frequently people give up drying their hands and wipe them on their clothes instead, but hand hygiene is a key part of infection control and drying hands after washing is a very important part of the process.
A study by researchers at the University of Bradford looked at different methods of hand drying, and their effect on transfer of bacteria from the hands to other surfaces. Snelling, et al. (2010) sought to compare an ultra-rapid hand dryer against warm air dryers to determine the amount of bacterial transfer after drying the hands, as well as the impact on bacterial numbers of rubbing hands during dryer use. The research was published in an early online edition of the Journal of Applied Microbiology.
The different methods included paper towels, traditional hand dryers, which rely on evaporation, and a new model of hand dryer, which rapidly strips water off the hands using high velocity air jets. In this study the researchers quantified the effects of hand drying by measuring the number of bacteria on different parts of the hands before and after different drying methods. Volunteers were asked to wash their hands and place them onto contact plates which were then incubated to measure bacterial growth. The volunteers were then asked to dry their hands using either hand towels or one of three hand dryers, with or without rubbing their hands together, and levels of bacteria were re-measured.
Snelling and her team found that rubbing the hands together whilst using traditional hand dryers could counteract the reduction in bacterial numbers following handwashing. Furthermore, they found that the relative reduction in the number of bacteria was the same, regardless of the hand dryer used, when hands are kept still. When hands are rubbed together during drying, bacteria that live within the skin can be brought to the surface and transferred to other surfaces, along with surface bacteria that were not removed by handwashing. The researchers found the most effective way of keeping bacterial counts low, when drying hands, was using paper towels. Amongst the electric dryers, the model that rapidly stripped the moisture off the hands was best for reducing transfer of bacteria to other surfaces.
The researchers compared the efficacy of the Airblade dryer (manufactured by Dyson Ltd.) which uses two air knives to strip water from still hands, with two conventional dryers that use warm air to evaporate moisture while hands are rubbed together. The hands of 14 volunteers were contaminated by handling meat and then washed in a standardized manner. The researchers report that after using the dryers, fingers were pressed onto foil and transfer of residual bacteria enumerated. Transfers of 0107 CFU per five fingers were observed. For a drying time of 10 s, the Airblade led to significantly less bacterial transfer than the other dryers. When the latter were used for 30 to 35 seconds, the trend was for the Airblade to still perform better, but differences were not significant. In a second study, drying was performed after hand rubbing. Contact plates enumerated bacteria transferred from palms, fingers and fingertips before and after drying. When keeping hands still, there was no statistical difference between dryers, and reduction in the numbers released was almost as high as with paper towels. Rubbing when using the warm air dryers inhibited an overall reduction in bacterial numbers on the skin.
Snelling, et al. (2010) concluded that effective hand drying is important for reducing transfer of commensals or remaining contaminants to surfaces. Rubbing hands during warm air drying can counteract the reduction in bacterial numbers accrued during handwashing. The researchers add that a shorter drying time, facilitated by a dryer's technology, should encourage greater compliance with hand drying and help reduce the spread of infectious agents via hands.
Snelling says, Good hand hygiene should include drying hands thoroughly and not just washing. The most hygienic method of drying hands is using paper towels or using a hand dryer which doesnt require rubbing your hands together.
Reference: Snelling AM, Saville T, Stevens D and Beggs CB. Comparative evaluation of the hygienic efficacy of an ultra-rapid hand dryer vs conventional warm air hand dryers. Journal of Applied Microbiology. doi: 10.1111/j.1365-2672.2010.04838.x