According to the Mayo Clinic study, hot air dryers were shown to increase the number of all types of bacteria on the hands.
When hands were rubbed together, as is suggested on many devices, bacteria levels began to increase after 15 seconds of use, according to the study.
The jet air dryer also increased bacterial numbers, though not to the same levels as conventional hot air dryers. Still, the numbers were higher than evaporation.
Paper towels were the most effective at removing bacteria, especially from fingertips. Only a UV light was more effective at removing bacteria than paper towels, according to the study.
There were contrasting studies in this area, however. In one, hand dryers were shown to actually be superior to paper and cloth towels — though the field conditions have been called into question. In this study, researchers measured bacteria levels by pressing finger pads firmly onto the paper towel.
This is in contrast to how most people dry their hands with paper towels, which is typically done in a vigorous, rubbing motion over the hands (the act that is believed to physically remove bacterial loads from the hand — a main benefit of paper towels).
“Many studies have found friction to be a key component in hand drying for removing contamination,” the study says. “For example, (one study) reported that bacteria were removed from washed hands by the mechanical abrasive action of drying with paper towels.”
“The biggest thing is when you are drying your hands with paper towels, you have a physical action,” says Smith. “You are going to have the removal of soil, oils, and there is still abrasion to the surface to remove anything that may be residing on the skin. More importantly you remove the water that spreads germs.”
By Stephanie S. Beecher, Associate Editor