While many believe hot water is more effective than cool water when it comes to handwashing, the temperature of the water used is not related to how well pathogens are eliminated during the process, according to research in the Journal of Consumer Studies.

Becker's Hospital Review reports that researchers examined cleanliness of subjects' hands after washing in several different temperatures of water. While 70 percent of the test subjects believed hot water was more effective than cold water for hand hygiene, water as cold as 40 degrees Fahrenheit reduced bacteria on hands just as well as warmer water, according to a report on the study from National Geographic.

What's more, "warmer water can irritate the skin and affect the protective layer on the outside, which can cause it to be less resistant to bacteria," according to one of the study's authors. Skin irritation is one reason healthcare workers forgo hand hygiene, according to research published in late 2013.

The energy expended as a result of using unnecessarily warm water for hand washing is approximately equal to the annual carbon emissions of Barbados, according to the National Geographic report. Researchers recommended using water at a "comfortable" temperature to wash hands, rather than using hot water.