If you’ve ever been in a place or circumstance where hot running water wasn’t available for some reason, perhaps you had a vague sense when washing your hands in the only water available — cold — that they weren’t really getting clean. That’s probably because most of us learned in kindergarten that washing with hot, soapy water is imperative to kill germs. The belief is so ingrained that it’s been written in government regulations (at least in the U.S.) for years.
Even using soap with cold water may seem as if using hot water would do a better job, but is there any actual scientific evidence this is true? Here’s your answer: New research shows that if the water you’re using to wash your hands is lukewarm or even cold, it does just as well as hot to remove bacteria. It’s the length of time and the method that make all the difference.
The study, conducted at Rutgers University and published in the Journal of Food Protection,1 involved 21 participants and ended with an interesting conclusion: Whether they washed their hands in 60-, 79- or 100-degree (Fahrenheit) water, there was no difference in the “clean” they attained when they lathered their hands and washed them for 10 seconds.
But here’s the kicker: Every one of those individuals had high levels of E. coli bacteria “applied” to their hands. Although the scientists in charge used a “nonpathogenic” strain of the bacteria, each subject was asked to wash their hands using several different water temperatures and for varying lengths of washing time.
They used cold, warm or hot water, between half a milliliter and 2 milliliters (ml) of soap and washed for anywhere from five to 40 seconds. They repeated the experiment 20 times over a six-month period. Time added:
“When the researchers analyzed the amounts of bacteria left on hands after washing, they found that water at all three temperatures worked equally well. So did the different amounts of soap used, although they say more research is needed to determine what type of soap is best.”2