NEW BRUNSWICK, N.J. — Hot or cold — how do you take your water when washing your hands? Many believe that the warmer the temperature, the more germs will be erased. Scientists have put this one to rest though: a new study finds that cooler water is just as effective as hot water in removing bacteria.
At the end of the day, finding a comfortable temperature is the way to go, the study concludes.
Researchers at Rutgers University recruited 10 men and 10 women from the local community and applied a significant amount of a harmless bacteria to their hands numerous times over a six-month period. Each individual then washed his or her hands in cool water (60 degrees), warm water (79 degrees), or hot water (100 degrees).
They were also instructed to use one of three different amounts of soap.
During the test period, the individuals were barred from using antimicrobial soap or any hand sanitizer, and the authors checked to ensure the volunteers weren’t using any cosmetic products that might compromise their skin quality or levels of bacteria.
After samples were taken following each washing, the researchers discovered that the temperature of the water made no difference in germ removal, nor did the amount of soap being used.
“People need to feel comfortable when they are washing their hands but as far as effectiveness, this study shows us that the temperature of the water used didn’t matter,” says study co-author Donald Schaffner, a distinguished professor and extension specialist in food science at the university, in a news release. “Also we learned even washing for 10 seconds significantly removed bacteria from the hands.”
The finding may of particular interest to restaurant workers. Food and Drug Administration guidelines currently suggest that water at establishments measure at 100 degrees (F) for handwashing.
Schaffner said he hopes the FDA will revisit the temperature policy during their next scheduled conference in 2018.
“I think this study indicates that there should be a policy change,” he says. “Instead of having a temperature requirement, the policy should only say that comfortable or warm water needs to be delivered. We are wasting energy to heat water to a level that is not necessary.”
On that same token, those interested in their home energy use should be happy with the results of the study as cold water requires less energy than hot water.
The study’s findings were published in June in the Journal of Food Protection.