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Proper handwashing technique

People typically wash their hands seven times a day in the United States, but they do it at a far higher temperature than is necessary to kill germs, a new study says. The energy waste is equivalent to the fuel use of a small country.

Photograph by Gaetan Bally/Keystone/Corbis    

Brian Clark Howard

National Geographic

Published December 12, 2013

It's cold and flu season, when many people are concerned about avoiding germs. But forget what you think you know about hand washing, say researchers at Vanderbilt University. Chances are good that how you clean up is not helping you stay healthy; it is helping to make the planet sick.

Amanda R. Carrico, a research assistant professor at the Vanderbilt Institute for Energy and Environment in Tennessee, told National Geographic that hand washing is often "a case where people act in ways that they think are in their best interest, but they in fact have inaccurate beliefs or outdated perceptions."

Carrico said, "It's certainly true that heat kills bacteria, but if you were going to use hot water to kill them it would have to be way too hot for you to tolerate."

She explained that boiling water, 212°F (99.98°C), is sometimes used to kill germs-for example, to disinfect drinking water that might be contaminated with pathogens. But "hot" water for hand washing is generally within 104°F to 131°F (40°C to 55°C.)  At the high end of that range, heat could kill some pathogens, but the sustained contact that would be required would scald the skin.

Carrico said that after a review of the scientific literature, her team found "no evidence that using hot water that a person could stand would have any benefit in killing bacteria." Even water as cold as 40°F (4.4°C) appeared to reduce bacteria as well as hotter water, if hands were scrubbed, rinsed, and dried properly.

In fact, she noted that hot water can often have an adverse effect on hygiene. "Warmer water can irritate the skin and affect the protective layer on the outside, which can cause it to be less resistant to bacteria," said Carrico.

Using hot water to wash hands is therefore unnecessary, as well as wasteful, Carrico said, particularly when it comes to the environment. According to her research, people use warm or hot water 64 percent of the time when they wash their hands. Using that number, Carrico's team calculated a significant impact on the planet.  (See related “Quiz: What You Don’t Know About Climate Change Science.”)

"Although the choice of water temperature during a single hand wash may appear trivial, when multiplied by the nearly 800 billion hand washes performed by Americans each year, this practice results in more than 6 million metric tons of CO2 equivalent emissions annually," she said.

That's roughly equal to the emissions of two coal-fired power plants, or 1,250,000 passenger vehicles, over the course of a year. It's higher than the greenhouse gas emissions of small countries like El Salvador or Armenia, and is about equivalent to the emissions of Barbados. If all U.S. citizens washed their hands in cooler water, it would be like eliminating the energy-related carbon emissions of 299,700 U.S. homes, or the total annual emissions from the U.S. zinc or lead industries. (See related, "Six Stealthy Energy Hogs: Are They Lurking In Your Home?")

Gauging Hand Washing

Carrico said she decided to look at hand washing after searching for easy ways to reduce climate change emissions. "Sometimes simply educating people can go a long way toward changing behavior and reducing emissions," she said.

By zeroing in on hot water, she focused on an important source of emissions and potential waste. After heating and cooling, water heating is typically the largest energy user in the home because it is necessary for so many domestic activities, says the American Council for an Energy-Efficient Economy (ACEEE). In both the United States and European Union, hot water heating accounts for 15 percent of home energy use. But homeowners often keep their hot water heaters turned up to a temperature far higher than is necessary for most household tasks, which efficiency experts says is no more than 120°F (48.9° C.) Every 10°F (5.6° C) reduction in water temperature will generally save 3 to 5 percent on water heating costs, says ACEEE. (How much can you save by switching lighting at home? Try the Light Bulb Savings Calculator.)

To address this issue, Carrico started looking at common activities like washing clothes and dishes. A 2011 study by Norwegian researchers found that washing clothes at 86°F (30°C) cleans clothing just as effectively as the more commonly used 104°F (40°C), uses 30 percent less energy, and reduces wear and tear on the garments.

But little study had been done on the energy and emissions impact of hand washing, an activity typically repeated seven times a day among residents of the United States.

So Carrico teamed up with Micajah Spoden, a research analyst at Vanderbilt; Michael Vandenbergh, a professor of law and director of the Climate Change Research Network at Vanderbilt; and Kenneth A. Wallston, a professor of psychology at the Vanderbilt School of Nursing. The researchers surveyed 510 American adults from around the country, and asked them questions about their hand washing behaviors and perceptions. Questions included how often they wash their hands, for how long, how hot the water is, and so on.

The researchers found that close to 70 percent of respondents said they believe that using hot water is more effective than warm, room temperature, or cold water, despite a lack of evidence backing that up, said Carrico. Her study noted research that showed a "strong cognitive connection" between water temperature and hygiene in both the United States and Western Europe, compared to other countries, like Japan, where hot water is associated more with comfort than with health. (See related, "Four Ways to Look at Global Carbon Footprints.")

The researchers published their results in the July 2013 issue of International Journal of Consumer Studies. They recommended washing with water that is at a "comfortable" temperature, which they noted may be warmer in cold months and cooler in hot ones.

Official Recommendations

In their official guidelines on hand washing, the Centers for Disease Control and Prevention and the World Health Organization don't actually specify a water temperature. The agencies do recommend using soap and water and scrubbing vigorously, for at least 20 seconds. (The CDC has even suggested singing the song "Happy Birthday" to yourself in your head, to mark the time.) When you are done, dry your hands thoroughly, the agencies say.

The point, said Carrico, is to wash well and wash often, not to worry about the water temperature.

A problem, however, is that some public health organizations still recommend elevated water temperature. For example, the authors noted, the Food Code of the U.S. Food and Drug Administration (FDA), a model meant to guide the local authorities who enforce health standards in restaurants, recommends that hand-washing sinks be equipped to provide water at a temperature of at least 100°F (38°C.)

A doctor with the Florida-based American Association of Public Health Physicians, who asked not to be named because she isn't authorized to speak to the media, told National Geographic that the association does not have any guidelines on water temperature when it comes to washing hands. She said she is not surprised by the results of the Vanderbilt study, however. She added that, when it comes to food preparation, the FDA has also recommended that no bare skin touch food, regardless of hand washing, since no amount of scrubbing can eliminate all traces of  norovirus and hepatitis-A.

Todd Sack, a Florida physician with the Council for Healthy Floridians of the Florida Medical Association, told National Geographic that he routinely tells doctors that they don't need to use hot water to wash their hands. Sack provides this information on his group's website and in seminars on how the health-care industry can go greener and save money.

"You don't need hot water, you need soap, water, and friction," said Sack. He added that the Escambia County Health Department in Pensacola, Florida, decided to turn off the hot water heaters in its five clinics two years ago, after a review of the literature provided no evidence that hot water was better.

"They are saving 2,500 dollars a year per clinic now, which they use to buy recycled paper, a Prius, and other environmental projects," he said. "They have full medical clinics, including an AIDS clinic, so they are serious about this. They have no hot water."

When asked if he has encountered much resistance from the medical community to turning down the water temperature, Sack said he hasn't encountered any pushback per se, just inertia. "It's hard to get doctors to talk about anything," he said.

Carrico admitted that "some people may have a negative reaction" to changing their hygiene routine. But, she added, "With any change you are going to have some small backlash effect, but most often it is not going to make up for the benefits that come from broader public education."(See related: "Pro-Environment Light Bulb Labeling Turns Off Conservatives, Study Finds")

She added, "While behaviors like hand washing don't account for a large source of emissions, they do play a role in meeting emissions targets and they are one more example of something people can do." (Energy-wise or an energy waster? Test yourself with our Personal Energy Meter.)

Follow Brian Clark Howard on Twitter and Google+.

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

66 comments
Matthew Horbacz
Matthew Horbacz

This article is horribly written. It is basically telling people "washing your hands in cold water is just as effective as washing them in hot water!" This is FALSE!! It is true that hot water does not kill bacteria. Only boiling water can do that. HOWEVER whenever you wash something, whether it be your hands or dishes, you are not killing any bacteria. You are simply removing them from the surface. Hot water is able to loosen bacteria much easier than cold water. Next time you have a greasy dish, try washing it with cold water...then try again with hot water. The bacteria is still alive, but it is not on the plate anymore! Cold water will not remove the bacteria from the plate. I never comment on articles, but the misleading information presented by this article really got me annoyed. I expect better articles from National Geographic...

B Scott
B Scott

Everyone that agrees with this article needs to rip out their water heater no matter what energy source is heating it. Enjoy your cold showers, wash your dishes and clothes in cold water and then everything else you do. Boiling water for cooking also wastes energy so get use to soaking your noodles in cold water for a few hours.

If people are more likely to wash their hands when there is warm water vs cold water, then there's your health benefit. Enough said.

Keith Lurie
Keith Lurie

Water should be solar heated, warm water improves the cleaning ability, and reduces time.

99% of bacteria is actually good for us, so we kill it all because of fear of the 1%.

Hospitals are full of a variety of disease, and hand washing is vital, - in your home, there is very little that can make you sick, and it's not such a big deal.  Improve your immune system, and let it handle germs!

Ben Carwana
Ben Carwana

Even before I read this I was using cold water because it took so long for the water to heat up

Hermann Scheuber
Hermann Scheuber

As cold water isn't better then warm water - I use always warm water to clean my Hands.

Larry Evans
Larry Evans

Anyone who has been paying attention will note that almost every NG article contains a gratuitous reference to "climate change".


Can't decide if it's just lazy journalists or journalistic malpractice.

Kermit Horn
Kermit Horn

Experts on Legionnaires Disease insist on our hot water tanks having a minimum temperature to avoid the lethal bacteria from forming in them. So, wash hands in cold water but don't turn down the temp in the hot water tank!  :)

Mohan Padaki
Mohan Padaki

Man has made ( will be certainly be doing) his life more miserable, without knowing the consequences of making ones life more comfortable OR luxurious. 

aicha mina
aicha mina

when it's cold i used to wash my hands in hot water..... bt from now... never!!!
anyway. thanx. new information

Gene Lee
Gene Lee

Maybe the reason for people to use hot water to wash hand are the cold weather. I  used to wash hand in cold water. 

arun kapur
arun kapur

good job in exploding a myth - thanks

Robert Gaertner
Robert Gaertner

Well the water may not directly kill germs but warmer water aids in reverse soaponification which removes more grease which is how we rid our hands of germs, by washing them away with our hand oils. Does this study test the cultures from the hands exposed to the same conditions? Does it look at human behavior to find out if warmer hands cause people to wash thair hands longer? If not I find it highly dubious.

Anna Eidson
Anna Eidson

Sadly, scientists have come up with so many contradictory studies that I no longer give credence to any of them.  Why are medical utensils sterilized?  Why do we wash dishes in hot water? Why do we boil water in third world countries?  Perhaps I'm horribly misguided, but I thought it was all to kill germs and bacteria.

M D
M D

Information from physicians who specialize in allergy treatments state patients should wash bedding in hot, not cold water, to reduce allergens. Has anyone heard of research verifying whether this does indeed reduce allergens?

M D
M D

Physicians specializing in allergy issues have current literature that states people with allergies should wash all bedding in HOT not cold water to reduce allergens. Wonder if this info has been based on scientific research...

Bob Setliff
Bob Setliff

If this is true then WHY does EVERY Public Health Office, Public Health Organization, Doctor, and Hospital in the country say to wash your hands in soap and HOT water for at least 20 seconds?

Bob Setliff
Bob Setliff

If this is true then WHY does EVERY Public Health Office, Health Organization, Doctor, and Hospital in the country say to wash your hands in soap and hot water for at least 20 seconds?

Barbara Sundberg
Barbara Sundberg

Fascinating; another myth blown! No hurry to replace my water heater that only produces "luke warm," now!

David Dinneen
David Dinneen

Never knew this before. Only cold water from now on.

Hamera Aisha
Hamera Aisha

The choice between washing hands with hot or cold water also depends on the climate of the region and other factors other than avoidance from the germs. Sometimes people prefer to wash hands with warm water in order to avoid  cold. 

michael campbell
michael campbell

It is great to save energy and money, but i believe that is is somewhat irresponsible to be so focused on savings while omitting clear data on the impact on the effect on health.  I understand the enthusiasm on saving energy, but some additional detail on proper hand washing as a public awareness campaign should be included as a major part of this report. I say this because in many public washrooms around the country (USA), the soap dispensers provide very little soap which may be related to the expectation that 'warm' water in many public washrooms may be sufficient to stop the germs.


Also, I believe that in the same way that bacteria are becoming resistant to hand sanitizers and making our world less safe, bacteria may also become resistant to these 'warm water' hand washing temps 'too cool to kill'.



Regina Swinnen
Regina Swinnen

I always wash my hands with tap water not heated nor cooled. Warmer in summer, colder in winter. But it's just the hands so don't even care for warmer water. Cleaning the home is considered better when using hot water out here but cold water cleans just as good. So I only do dishes and laundry with warm water depending on what I wash how hot it has to be. For shower I have an electrical boiler which I only put on a few hours at night and if I need to do dishes just use a small boiler.My electric bill the first time moving in here was calculated to cost over 70 eur per month and my landlord told me I'd really need that. Year two my pre paid is at 10 eur per month and I still get money back each year. I use the night benefits, don't leave lights on unnecessarily except for my laptop. Don't have TV or game consoles so my laptop is really the only device aside from aenergy effecient fridge that is on day and night. I don't play games on my phone so my iphone battery easily lasts 3-7 days.And I still feel bad for the excessdrinkable  water flushed down the toilet despite my water cost being integrated in my stable rent while only flushing the minimum of water down. For drinking I use tap water all the time,leave it stand at room temperature and I rarely consume fast food or sodas. Instead of using light bulbs in the evening to have background light I often light a single candle. The only way I can consume even less energy is living totally in nature without any flowing water or electricity (which I've done before and will do again)

Greg Chick
Greg Chick

I always wash my clothes in cold water,  as a matter of fact,  I use an HET front loading washer and I never have a smelly machine.  Now is this because all the people who have smelly HET washers use hot water?  or is it that they let the clothes pile up and get "ripe" before washing them?   So now to get to hands, if I wash them well and use cold water,  I bet I will have no issues with bacteria.  My point is behavior is often an issue, we really should avoid letting our laundry pile up till it smells,  and we need to actually wash our hands,  not just go thru some patronizing motions.  

By the way,  my wife and some others in my home town have formed a non profit org. and have bought and I have installed $10,000 worth of vandalproof soap dispensers in the local high schools and a middle school where the attendance last yr. was low from students missing from being sick.   $380,000 was lost in per diem funding from Ca. state funding.  40 soap dispensers were knocked off the walls in student bathrooms and no soap was possible to be used.   I put in antibacterial foam dispensers and am sure that hot water has never actually arrived in the lav. basins.  The issue will be watched closely.   My wife is an MD Pediatrician and has several hundred patients in these schools we up graded.  I will keep you posted.      

Trevor Ceniviva
Trevor Ceniviva

I can't tell if people here are afraid of germs or just hating on the environment for the sake of it. Whether or not you care about the environment, you could save money on your bills by washing your hands in cooler water (notice neither I nor the article said cold water) and you won't suffer germs any more than you already are.

Nate Jones
Nate Jones

This article talks about saving energy and using cold water instead of 104-130*F water which is useless for hand washing. The world could save a lot of energy by just doing this one thing. It does not say go live in the forest! It does not say you have to use cold water ONLY. It does not say take a shower at 40*F.  I find it funny how most comments go way off on what this article is trying to say.

Simon Gray
Simon Gray

I have to wonder about the soap though. In cold water it doesn't lather well - is the soap less effective with cold water, and if it is less effective, is it significant?

C D
C D

Sounds like the "small backlash effect" is alive and well in these comments. Always amazing how defensive people get when their petty comforts and conveniences are perceived to be threatened. The article isn't talking about grease and oil....most handwashing occurs after using the restroom and yes, hot water is entirely unnecessary there. It's just one small thing we can control and do better and small incremental changes can make an impact. Your children, children's children, friend's children etc. may thank you one day for sacrificing small comforts, so they can moderately enjoy themselves as well.

Jay Cwanek
Jay Cwanek

Welcome to the 11th century.  Aren't you glad you voted environmentalist for the last 25 years?

Laura Griffin
Laura Griffin

 These ridiculous stories just never stop.  Really?  Stop using warm/hot water to wash your hands?  


As soon as I start reading that the authors of these nonsense articles live in the forest, completely naked, surviving on fallen leaves, using a piece of slate to write their stories and never ever getting into a vehicle of any sort in their lives, then I will start buying the B.S. they're selling. 


Otherwise, this nonsense needs to stop.  Enough is enough.  This has gone past the lunatic stage to complete and utter insanity.

Robert Harvey-Kinsey
Robert Harvey-Kinsey

Cold water and soap does not remove fats, grease, or oils. Scrubbing enough to removed those with cold water would tear your skin apart. If the water is very cold it hurts. Germs are not the only reason we wash our hands or homeowners need hot water.

kelly d
kelly d

Most blokes I know bearly splash their hands with water so I guess I can't complain any more they are saving energy 

Chris Samuelian
Chris Samuelian

Not True. Not True. An irresponsible story, in fact. Soap naturally kills bacteria by exploding it, and its coverage is directly related to the temperature of water: the higher the temperature the more bacteria soap kills. This was explained to me by my cousin who is a PhD in biological chemistry.

The premise of the article is biased toward energy usage but dangerous in terms of a pandemic. The magazine should be more careful.

kevin woolf
kevin woolf

People use hot/warm water when they wash to increase the solubility of oils and residues they want to wash off, not to kill germs.  

David B.
David B.

@Anna Eidson Read the article. Boiling water does kill germs. Hot water from the tap is not hot enough to kill them, so it's just wasted.

Paul Kounine
Paul Kounine

@michael campbell Please don't fall for the myth that hand sanitizers create super bugs and drug resistant bacteria. This is simply false. Antibiotics and hand sanitizers based on alcohol solutions kill bacteria in COMPLETELY different ways. Rest assured, your alcohol gel based hand sanitizer isn't going to produce any drug resistant bacteria.

Rebecca Hovis
Rebecca Hovis

You may want to look into the recent FDA notes about anti-bacterial soaps.

Joe Salata
Joe Salata

As Sartre said, "Hell is other people."

Jay Cwanek
Jay Cwanek

There is a difference between "small backlash" and a whip lashing my friend.  My guess is that you never lived in a place with no running water, as I have.  Once you've left that 11th century, you don't go back there out of petulant self-hatred at your greed in leaving.  Always amazing how easy (and petty and offensive) it is for some folks to ask those who have been genuinely poor to go back to it.

Andrew Olmsted
Andrew Olmsted

A problem, however, is that some public health organizations still recommend elevated water temperature. For example, the authors noted, the Food Code of the U.S. Food and Drug Administration (FDA), a model meant to guide the local authorities who enforce health standards in restaurants, recommends that hand-washing sinks be equipped to provide water at a temperature of at least 100°F (38°C.)"  SERIOUSLY? You included this as part of your argument? WE DON'T NEED TO USE HOT WATER....EVEN THOUGH HEALTH ORGANIZATIONS AND THE FDA SAY WE SHOULD......CLUELESS.


C D
C D

@Jay Cwanek No one is asking you to give up running water, Jay. This is about being less wasteful where we can and remembering to leave enough for those who come after us (I am certain they would not appreciate poverty either and I am very sorry you have had to experience it).

Jay Cwanek
Jay Cwanek

Everything that starts in "asking" ends in "regulating".  Abjure now any future regulations preventing people from washing their hands in THEIR comfort zone, not yours, and we can take your intent as harmless indeed.

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