Rubbing hands together under warm air dryers can counteract bacteria reduction

**Snelling AM. J Appl Microbiol. no. doi: 10.1111/j.1365-2672.2010.04838.x**

An ultra-rapid hand dryer that does not require hand rubbing eliminated significantly more bacteria than traditional dryers, according to a comparative study.

"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 doesn't require rubbing your hands together,” said Anna Snelling, PhD, of Bradford University, in a press release.

Snelling and colleagues tested the Dyson Airblade dryer, which uses two high velocity air “knives” to remove excess water from hands, and two models of traditional warm air dryers, the A5 and Turbodry, which blow warm air downward while the hands are rubbed together.

The hands of 14 subjects were contaminated by handling uncooked chicken meat for 45 seconds. The subjects then washed their hands with water and a single squirt of nonmedicated soap for 60 seconds.

For the first part of the study, the subjects dried their hands using each dryer for 10 seconds. They rubbed their hands together while using the standard dryers, but did not do so when using the Airblade, as per the product’s instructions. The subjects then pressed their fingertips into aluminum foil, which was analyzed for bacteria transfer.

Despite thorough handwashing and drying, the researchers observed transfers of up to 10⁷ per five fingers. Hands dried with the Airblade had significantly less bacterial transfer than the other hand dryers (P<.05 range .0003-.0015). When the drying time with the traditional dryers was increased to 30 to 35 seconds, the differences were no longer significant (P>.05 range .1317-.4099).

For the second part of the study, hand drying was performed both with and without rubbing. Bacteria rates on the subjects’ hands were recorded with contact plates before and after drying. The researchers noted that, when the subjects did not engage in hand rubbing, bacteria reduction was statistically similar across all machines, and was almost as effective as using paper towels. However, when the subjects rubbed their hands under the A5 and Turbodry, the process of rubbing “generally inhibited the overall reduction in bacterial numbers release from the surface of the skin,” the authors wrote. In most cases, the difference between rubbing and not rubbing were statistically significant (P<.05).

“It appears that the act of briskly rubbing the hands together disturbs the outer skin squamae and brings bacteria from within the pores to the surface,” the researchers wrote.