Mom always said hot water kills more germs.
Maybe you didn’t feel like waiting for the tap to heat up. Maybe it was hot outside so you turned on the cold water to cool down. Maybe you just prefer the icy blast of cool water. Either way, when your mom caught you washing your hands with cold water, she gasped.
“You have to use hot water,” she reprimanded. “Hot water kills more germs.”
Was mom right? Is hot water the only way to clean your germy hands? Even worse, were you actually wasting your time washing your hands with cold water?
The science is in, and it looks like mom has found herself in “hot water.” According the the Centers for Disease Control and Prevention (CDC), the best way to ensure clean hands is to wash with clean, running water and soap (as stagnant water can collect bacteria). The water temperature, it turns out, makes very little difference.
Is Hot Water Doing Your Hands Any Favors?
In fact, washing your hands with steamy water can be more harmful than good. For years, rules for food service workers specified that handwashing should be done with hot water. The idea was that it would kill more germs, reduce the risk of cross-contamination, and stop the spread of infections.
The problem is, all that hot water damaged the skin, and employees complained of dry, itchy, irritated skin. That’s because water at higher temperatures strips the skin of its natural oils, and it can even trigger symptoms for people with skin conditions like eczema. Because of the adverse effects on the skin, washing with hot water started to become a deterrent for consistent handwashing among food service employees.
A study in the journal Food Service Technology set out to find if the hot water was really necessary. The researchers contaminated participants’ hands with E. coli and then measured the amount of germ activity remaining after washing with warm or hot water.
It turns out, washing with hot water yielded no significant difference. For this reason, the CDC says to adjust the water temperature to your comfort level—preferably warm or cold.
Turn Down the Temps
Your skin health isn’t the only reason to turn down the water temperature. Hot water requires more energy use and results in more greenhouse gas emissions, according to a 2013 study by researchers at the Vanderbilt Institute for Energy and Environment in Nashville, TN.
According to the study, about 70 percent of surveyed Americans believe that hot water kills more germs, and this comes at a cost to the environment. The study found that if guidelines were updated to promote washing hands at a lower temperature, it would prevent one million metric tons of carbon dioxide emissions a year.
Minimizing greenhouse gas emissions is not simply an environmental effort: It affects public health as well. According to the CDC, air pollution can cause or trigger respiratory problems, such as asthma and COPD. It can also be harmful for heart health and increase the risk of heart attack or stroke.
OK, so mom wasn’t right, but we won’t blame the messenger. To have clean hands and help prevent colds, just keep these rules by the CDC in mind:
Wash with clean, running water and use soap. (Learn more about what kind of soap to use here.)
Don’t forget to lather up the backs of your hands, between your fingers, and under your fingernails.
Scrub for at least 20 seconds—the amount of time it takes to sing “Happy Birthday” twice.
Rinse well and dry with a clean towel or air dry them.
Air quality. Atlanta, GA: Centers for Disease Control and Prevention. (Accessed on September 6, 2018 at https://www.cdc.gov/air/air_health.htm.)
Carrico AR, Spoden M, Wallston KA, Vandenbergh MP. The environmental cost of misinformation: why the recommendation to use elevated temperatures for handwashing is problematic. Int J Consum Stud. 2013 Jul 1;37(4):433-41.
Eczema and bathing. San Rafael, CA: National Eczema Association. (Accessed on September 6, 2018 at https://nationaleczema.org/eczema/treatment/bathing/.)
Michaels B, Gangar V, Schultz A, Arenas M, Curiale M, Ayers T, Paulson D. Water temperature as a factor in handwashing efficacy. Food Service Technology. 2002 Oct 1;2(3).
Show me the science - how to wash your hands. Atlanta, GA: Centers for Disease Control and Prevention. (Accessed on September 6, 2018 at https://www.cdc.gov/handwashing/show-me-the-science-handwashing.html.)