Scientists say they’ve figuratively and literally thrown cold water on the theory that washing hands with hot water is more effective at killing germs.
A small study with 20 participants found that people using water at 15C to wash had hands as clean as those who washed with water heated to 38C, the BBC reports. This is good news for restaurants and hotels, where electricity bills could be cut, among others.
Scientists at Rutgers University-New Brunswick wanted to test if the popular assumptions on the benefits of using hot water, and the official guidelines on hot water use in the US food industry, were true.
They asked 20 people to wash their hands 20 times each, with both cold and hot water. The participants were also asked to use varying amounts of soap, from 0.5mm to 2mm.
Before the participants washed, their hands were swiped with harmless germs.
According to the researchers, there was no significant difference in the amount of bugs removed from the hands as the water temperature or the volume of soap changed.
Donald Schaffner, lead on the study, says,
People need to feel comfortable when they are washing their hands but as far as effectiveness [goes], this study shows us that the temperature of the water used did not matter.
However, the researchers did admit that their study sample was small, and that more extensive studies are needed to determine the best ways to wash potentially harmful bacteria and germs off hands – and the rest of the human body.
The British National Health Service recommends that people wash their hands in either cold or warm water. It emphasizes that hands should be washed and rubbed vigorously for at least 20 seconds – as long as singing “Happy Birthday” twice, and that enough soap should be used to cover the whole surface of both hands.
The study was published in the Journal of Food Protection.
