Scientists at NJ’s Rutgers University-New Brunswick have poured cold water on the theory that washing hands with hot water kills more germs than unheated water. In a study, they wanted to determine if popular assumptions about the benefits of warm or hot water and official guidance on hot water given to the food industry in the United States held true.
They asked 20 people to wash their hands 20 times each with water that was 59°F, 79°F, or 100°F. Before they started the tests, the subjects’ hands were covered in harmless bugs, and the researchers noted that there was no difference in the amount of bugs removed based on the temperature of the water.
“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,” said Donald Schaffner, PhD, of the university’s department of food sciences.
The researchers do acknowledge that their study is small and say more extensive work is needed to determine the best ways to remove harmful bacteria.
In the United Kingdom, National Health Service experts say people can use cold or hot water to wash their hands. They say hands should be washed for at least 20 seconds and stress the importance of using enough soap to cover the whole surface of the hands. Their guidance focuses on rubbing hands together in various ways to make sure each surface of each hand is clean.
According to experts, washing your hands properly should take about as long as singing “Happy Birthday” twice (about 20 seconds).
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