Moms have been telling their children for generations to wash their hands with soap and hot water. This is so instinctive to most of us that we don’t even question whether or not mom’s advice was right. But that did not stop researchers from Rutgers University from looking into things. What they discovered about water temperature during the hand washing process might surprise you.
So, is hot water necessary for proper hand washing? That depends on what you’re trying to accomplish. In terms of killing germs, no. But if you’re looking to kill germs and get maximum benefits from your soap, then water temperature does matter.
Soap and Water Put to the Test
Rutgers University researchers developed a test in order to find out just how effective hand washing is. They wanted to know what role water temperature, soap volume, and time all played in removing microbes from the hands. Their test involved 20 volunteers who washed their hands 16 times under controlled conditions.
The researchers set up different scenarios that accounted for different water temperatures, different volumes of soap, and different amounts of time spent washing the hands. Then they put the volunteers through each scenario and measured the results. What did they discover? That the temperature of the water had absolutely no effect on how well their soaps dealt with microbes.
This suggests that if your only concern for hand washing is to remove germs, you can use any temperature water you like. It doesn’t have to be hot. It doesn’t even have to be warm. Cold water will still do the trick. But there is a caveat here: the type of soap you use matters.
Time and Lather
Researchers discovered that what really mattered in their hand washing scenarios was time. The amount of time spent soaking the hands in the soap solutions is what really made the difference. They also noted that lathering is important. Lather is what creates the surfactant effect that makes soap such a good tool for getting rid of microbes.
Now, this is where water temperature might make a difference. Note that the Rutgers experiment utilized a solution in which soap and water were already mixed together. Students soaked their hands in those solutions for given amounts of time. But that’s not the way most of us wash our hands; we don’t soak them in liquid solutions.
Most of us wash our hands with bar soap or a liquid dispensed from a plastic container. In either case, we have to create the lather with our hands. It turns out that water temperature does play a role here.
According to Kuhdoo Soap, an artisan soap company based in Austin, Texas, soap tends to lather better with warmer water temperatures. This is especially true of natural soaps made with plant-based oils or animal fats. Hot water softens natural soaps so that they lather more easily and quickly.
Kuhdoo Soap’s beer soap bar is a good example. You can use it to wash in water of any temperature, but it will lather more quickly and thoroughly if you use warm or hot water.
Not Necessarily Bad Advice
In the end, mom’s advice wasn’t necessarily bad. Feel free to use cold water to wash your hands if you’re willing to put in a little bit of extra time in order to get rid of all those nasty microbes. Use cold water if you want to save energy, as well. But if you want your hand soap to lather up quickly and more thoroughly, warm or hot water is the better choice.