Like a lot of people I am more inclined to believe research that is in accord with my prior beliefs. Put another (Bayesian) way, I don’t have to change my beliefs much on the basis of evidence. That means I don’t question the evidence rigorously. So with that warning, here’s a story I instinctively believe because it accords with my prior beliefs — and preferences. It has to do with washing your hands after using a public bathroom.
To be clear at the outset: I always wash my hands after using the bathroom. I’m not sure what the actual evidence for disease transmission is but I consider it an aesthetic matter and good etiquette. But I also hate the hot air hand dryers many public bath rooms have installed instead of providing towels. Yes, I know there’s a solid waste issue. But it takes longer and it doesn’t leave my hands feeling clean. Now a study of paper towels, warm air dryers and the unique Dyson Air Blade hand dryer, done at the University of Westminster and paid for by the European Tissue Symposium, has validated my prior preferences. Note that the European Tissue Symposium doesn’t refer to biological tissue researchers. These are makers of paper towels, so consider the source. With that out of the way, here’s what they found:
There were four parts to the study: Part A looked at the drying efficiency of hand drying method; Part B involved counting the number of different types of bacteria on the hands before and after drying; Part C studied the potential contamination of other users and the washroom environment; and Part D took a bacterial sampling of Dyson Airblade dryers in public washrooms.
Paper towels and the Dyson Airblade were found to be equally efficient at drying hands, each achieving 90% dryness in approximately 10sec. However, the warm air dryer was considerably less efficient, taking 47sec to achieve the same level of dryness.
Twenty subjects (10 male and 10 female) were used in Part B. Three different agar growth media (nutrient, cystine-lactose-electrolyte-deficient and mannitol salt agar) were used to count and identify the bacteria on the fingerpads and palms before and after washing and drying.
Paper towels were found to reduce the number of all types of bacteria on the fingerpads by up to 76% and on the palms by up to 77%. By comparison, the Dyson Airblade increased the numbers of most types of bacteria on the fingerpads by 42% and on the palms by 15%. However, after washing and drying hands under the warm air dryer, the total number of bacteria increased by 194% on the fingerpads and on the palms by 254%.
The Dyson Airblade performed less well than paper towels and the warm air dryer in Part C in which the hands of 10 subjects were artificially contaminated with yeast suspension. During use, open agar plates were placed at 0.25m intervals from the hand-drying device up to a maximum of 2m. Yeast colonies that grew on the plates were counted.
The Dyson Airblade dispersed potential contamination to other users and the washroom environment to a distance of at least two metres, whereas paper towels spread contamination 0.50m and the warm air dryer 0.25m.
Part D showed that the Dyson Airblade dryers in the public washroom sampled were contaminated with large numbers of bacteria, including potential pathogens such as E. coli, staphylococcus and pseudomonas aeruginosa, particularly the bottom of the hand drying chamber
According to Keith Redway, senior academic in the department of Biomedical Sciences at the University of Westminster: ?The results of all parts of this study suggest that the use of warm air dryers and jet air dryers should be carefully considered in locations where hygiene is of paramount importance, such as hospitals, clinics, kitchens and other food preparation areas, schools, nurseries and care homes.? (Clean Room Technology [UK])
The Dyson Airblade folks are unhappy, saying the University of Westminster’s methodology was faulty and noting that this was paid for by the paper towel industry. I’m not able to judge with the information at hand (so to speak). But I’d much rather have a paper towel than an air dryer. Sorry, Dyson.