Could the very act of washing and drying your hands after using a public bathroom actually leave your hands covered in poop? According to the findings of a recent study appearing in the Applied and Environmental Microbiology Journal, the hand dryers (those that blow hot air when you place your hands under them) evaluated in 36 bathrooms on one university campus deposited up to 60 different colonies of bacteria on plates placed below them to capture microorganisms. Some of those bacteria were fecal matter.
Before you swear off washing and drying your hands in public restrooms, be assured this was the finding of just one study (although other previous research has uncovered some similar findings; see below). Also, there is more than one way to dry your hands after washing (including shaking them for several seconds and then using one [and only one] paper towel to dry-to be environmentally conscious.).
It’s also important to point out that the hand dryers in this study did not have HEPA filters installed, as some commercial models are so equipped. HEPA filters can remove significantly more pathogens than non-HEPA filters.
Current hand dryer and poop study
The study took place at the University of Connecticut and was conducted in 36 bathrooms (both male and female). Collection plates were placed under the dryers for about 30 seconds. The team found “between 18 and 60 different colonies of bacteria on each plate,” which led the authors to say that many bacteria, pathogens, and spores “could be dispersed throughout buildings and deposited on hands by hand dryers.”
One of the bacterial species found on all of the plates was Bacillus subtilis, a harmless bacterial strain found only in laboratory environments. The authors noted that these bacteria had spread through the air of the whole building and that within large buildings, potentially harmful bacteria may travel among the rooms. Hand dryers may be one way these bacteria make that journey.
Peter Setlow, one of the study’s lead authors, also explained that “Bacteria in bathrooms will come from feces, which can be aerosolized a bit when toilets, especially lidless toilets, are flushed.” Hand dryers take in bathroom air and dispense it at high speeds. Placing your hands under the dryer may expose them to more air than usual and thus more bacteria.
Previous hand dryer studies
This is not the first study to examine the cleanliness of air hand dryers in public restrooms. In a 2016 study published in the Journal of Applied Microbiology, an investigative team looked at how viruses were dispersed when people used a jet hand dryer, paper towels, or warm air dryers. The jet air dryers were significantly worse than the other two methods, as they sprayed 1,300 times more clumps of viruses than the paper towels.
Similarly, a 2014 study that appeared in the Journal of Hospital Infections looked at the efficiency of hand drying using jet air, paper towels, and warm air dryers and its impact on bystanders, the environment, and users. The participants (users and controls) had their hands coated in lactobacilli to simulate poorly washed scenarios.
The authors found that the jet air dryer resulted in a 4.5-fold greater level of bacterial contamination when compared with the warm air dryer and a 27-fold higher contamination when compared with the use of paper towels. The jet air dryer caused the most dispersal of bacteria droplets. Overall, the authors concluded that air dryers “may be unsuitable for use in healthcare settings, as they may facilitate microbial cross-contamination via airborne dissemination to the environment or bathroom visitors.”
How to best dry your hands in public washrooms
If air dryers are the only option, then use them. If paper towels and air dryers are offered, the paper towel is likely the better choice. However, to be environmentally conscious, one may want to follow the advice mentioned earlier: shaking one’s hands for several seconds and then using one paper towel to dry your hands (see video with demonstration by Joe Smith, former District Attorney in Umatilla County, Oregon). Washing your hands thoroughly with soap and water, however, is the best advice.
Best EL et al. Microbiological comparison of hand-drying methods: the potential for contamination of the environment, user, and bystander. Journal of Hospital Infection 2014 Dec; 888((4): 199-206
Hignett K. Restroom hand dryers suck up feces particles and spray them all over your hands. Newsweek 2018 Apr 10
Huesca-Espitia LC et al. Deposition of bacteria and bacterial spores by bathroom hot-air hand dryers. Applied and Environmental Microbiology 2018 Apr; 84(8): e00044-18
Joyce K. Bathroom hand dryers spraying poop on your hands, study finds. Fox News 2018 April 14
Kimmitt PT, Redway KF. Evaluation of the potential for virus dispersal during hand drying: a comparison of three methods. Journal of Applied Microbiology 2016 Feb; 120(2): 478-86