Many things that come out of a typical mother’s mouth seem scientifically iffy even to a kid, such as: “Your face is going to freeze like that!”
But, typical moms do occasionally say things that seem scientifically valid even to all-grown-up kids, such as: “Use warm water to wash your hands!” Even kid brains seem to believe that the water molecules we see in video animations that get all jumpy when heated would be do a better job of washing worm guts, for example, off your hands.
Well, turns out, scientists can determine no scientific basis for using warmer water to wash your hands. In fact, the CDC has stated that using warmer water might actually be worse for you and the environment: “The temperature of the water does not appear to affect microbe removal; however, warmer water may cause more skin irritation and is more environmentally costly.”
The CDC based its statement on studies that evaluated the effectiveness of handwashing with water of different temperatures.
One study, Water temperature as a factor in handwashing efficacy, stated: “After extensive statistical analysis of the results from the first set of experiments, it was determined that there was no significant difference in bacterial log10 reductions for either resident or transient bacteria at any of the test washing and rinsing temperatures.”
The study continued: “The results from both of these experiments are in agreement regarding the lack of hygienic benefits of washing hands at higher water temperatures and particularly at temperatures at the upper end of human tolerance, sometimes described as ‘hot as you can stand’.” As the water temperature gets hot, the study states, it begins damaging skin.
Another study cited by the CDC takes it a bit further:
“Multiple government and health organizations recommend the use of warm or hot water in publications designed to educate the public on best practices for washing one’s hands. This is despite research suggesting that the use of an elevated water temperature does not improve handwashing efficacy, but can cause hand irritation. There is reason to believe that the perception that warm or hot water is more effective at cleaning one’s hands is pervasive, and may be one factor that is driving up unnecessary energy consumption and greenhouse gas emissions.”
For more on the CDC’s recommendations on how to correctly wash your hands, click here.