Health: Hot and cold water are equally effective in removing bacteria

EagleHeadline | Jun. 21, 2017

The U.S. Food and Drug Administration recommends a minimum handwashing water temperature of at least 38 degrees Celsius (100 degrees Fahrenheit) to kill harmful bacteria, but a study by Rutgers University researchers concludes that washing hands in cold water is just as effective.

Instead of focusing on water temperature, researchers conclude that bacteria, even E. coli, can be removed from contaminated hands as long as proper handwashing technique and sanitary products are used.

Prof. Donald Schaffner and his team of researchers say their study could help cut down wasted energy used for heating water for handwashing in food establishments where the FDA strictly enforces the regulation.

There are many techniques claiming to be the most effective handwashing practice to eliminate harmful bacteria from our hands, but some open up contradictions while others lack scientific evidence to prove its legitimacy. To separate fact from fiction, Professor Schaffner and his colleagues challenged the popular assumptions and official FDA recommendations about handwashing through a series of tests done over a period of six months.

Challenging The Water Temperature Debate

Twenty individuals were asked to participate in the handwashing experiments wherein the research team contaminated the participants' hands with harmless bacteria (nonpathogenic E. coli) prior to washing their hands. The participants were then asked to wash their hands multiple times in water temperatures ranging from 15 degrees Celsius to 38 degrees Celsius (60 degrees Fahrenheit to 100 degrees Fahrenheit) and soap volume ranging from 0.5 milliliters to 2 milliliters.

Results showed that there was no significant difference in the amount of bacteria removed by cold and hot water. The only difference was in the energy that was used for heating up the water.

"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," Professor Schaffner said.

Revisiting Other Handwashing Techniques

Other handwashing techniques the team challenged involved beliefs about washing time, product formulation, and amount of soap used. The most basic but popular assumption was challenged: 100 degrees Fahrenheit water, 1 milliliter of non-antimicrobial (bland) soap, and 5-second lather time.

According to Professor Schaffner, their results showed that even the amount of soap used did not show significant results, and the bland soap killed as much bacteria as the tested antimicrobial soap with 1 percent chloroxylenol formulation.

"Also we learned even washing for 10 seconds significantly removed bacteria from the hands," Professor Schaffner said.

The only other improvement in bacteria reduction came from a 20-second lather time using bland soap compared to the basic 5-second wash.

Using the results of their study, the team recommends that FDA should consider a policy change when it comes to handwashing guidelines.

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