"It is true that heat kills bacteria," writes Amanda Carrico. "However, the level of heat required to neutralize pathogens is beyond what is considered safe for prolonged human contact." (Credit: Rocky Lubbers/Flickr)

Wash your hands! But turn down the heat

Washing hands in hot water offers no more hygienic benefits than using room temperature water—and significantly adds to greenhouse gas emissions worldwide.

If Americans en masse used tepid water instead of warm or hot to wash their hands, it could prevent annual greenhouse gas emissions totaling the equivalent of the United States’ lead industry or the entire output of a nation the size of Barbados, researchers say.

“Although the perception that hot water is more hygienic is based in some factual evidence . . . there are few, if any, hygienic benefits of using warm or hot water to wash one’s hands,” writes Amanda Carrico, research assistant professor at the Institute for Energy and Environment at Vanderbilt University.

“It is true that heat kills bacteria; however, the level of heat required to neutralize pathogens is beyond what is considered safe for prolonged human contact.”

In addition to global warming emissions, the use of elevated temperatures can cause skin irritation, which can lead to more bacterial colonization, not less.

Some soap may emulsify better with warmer water, but for most routine hand washes any such gains are irrelevant if hand washers follow a proper regimen of scrubbing, rinsing, and drying.

Other kinds of heated water use have been targeted by global warming researchers as potential ways to reduce greenhouse gas emissions, including laundry and dish washing.

No health benefits

The study on hand washing, published in the International Journal of Consumer Studies, shows that 69 percent of 510 people surveyed believed that hand washing with warm or hot water is more effective than room-temperature water.

“The average respondent reported using warm or hot water 64 percent of the time,” Carrico writes. “Although the choice of water temperature during a single hand wash may appear trivial, when multiplied by the nearly 8 billion hand washes performed by Americans each year, this practice results in over 6 MMt (million metric tons) of CO2 eq (equivalent emissions) annually.”

The temperature used during hand washing would be a good candidate for a public information campaign, the study says.

“Multiple federal and state organizations recommend using elevated water temperatures, in some cases citing its superior cleaning ability as the reason.

“There is no doubt that the intention of these organizations is to promote a behavior that is vital to protecting public health; however, the preponderance of evidence . . . suggests this recommendation provides no health benefit.”

The public should be encouraged to use a “comfortable” water temperature when washing their hands. In colder climates warm water may be most comfortable.

“Although the degree of temperature was not measured in the current study, these data suggest that those who hold accurate beliefs do choose against selecting warm or hot water at the faucet on many occasions.”

Source: Vanderbilt University

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4 Comments

  1. Smeagol

    Yeah it’s called common fucking sense and I swear to god this website lacks it every now and then. Some of these articles are just downright ignorant, obvious. redundant, or just plain obnoxious. Of course hot water washes your fucking hands better than room temperature. hot water melts and breaks away the dirt easier. It has nothing to do with people believing that the hot water is “killing bacteria”. We all know we can’t get water that hot without burning our hands. Jesus

  2. Smeagol

    Why don’t you pour some maple syrup all over your hands, or a plate even. Run room temperature water over them for awhile, and then run hot water over it for awhile. See which one dissolves first. No shit sherlock. This article is a failure.

  3. Kevin Hamill

    If tepid water was used then the risk of contracting legionella would increase as tepid water is the perfect temperature for legionella bacteria to breed.

  4. Rob N

    I disagree Smeagol, even disregarding your unprofessional language. Most people are concerned about bacteria for routine hand-washing, it’s not because their hands look dirty. On the rare occasions you have something else that needs cleaning, then by all means, use hot water if you want. But that’s separate from reducing germs.

    I pretty much always wash my hands with cold or cool water, and have been as healthy as any other person. It’s nice to know I have some justification in that approach.

    Kevin – Legionnaire’s disease is spread by inhaling or drinking bacteria that grows over time in standing water, not from casual contact or from washing hands. So the risk of contracting Legionnaire’s disease is unrelated to water temperature of hand washing.

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