Washing your hands in cold water works just as well as hot!

By Seriously Science | June 7, 2017 6:00 am

Photo: flickr/jar[o]

Photo: flickr/jar[o]

Conventional wisdom says that the best way to wash your hands is with soap and plenty of hot water. Well, prepare to have your mind blown! According to this study, it’s not the temperature of the water that matters for getting bacteria off your hands, or even whether the soap is antibacterial. What really matters is how long you lather, with 20 seconds being more effective than 5 seconds. I guess surgeons knew something we didn’t!

Quantifying the Effects of Water Temperature, Soap Volume, Lather Time, and Antimicrobial Soap as Variables in the Removal of Escherichia coli ATCC 11229 from Hands

“The literature on hand washing, while extensive, often contains conflicting data, and key variables are only superficially studied or not studied at all. Some hand washing recommendations are made without scientific support, and agreement between recommendations is limited. The influence of key variables such as soap volume, lather time, water temperature, and product formulation on hand washing efficacy was investigated in the present study. Baseline conditions were 1 mL of a bland (nonantimicrobial) soap, a 5-s lather time, and 38°C (100°F) water temperature. A nonpathogenic strain of Escherichia coli (ATCC 11229) was the challenge microorganism. Twenty volunteers (10 men and 10 women) participated in the study, and each test condition had 20 replicates. An antimicrobial soap formulation (1% chloroxylenol) was not significantly more effective than the bland soap for removing E. coli under a variety of test conditions. Overall, the mean reduction was 1.94 log CFU (range, 1.83 to 2.10 log CFU) with the antimicrobial soap and 2.22 log CFU (range, 1.91 to 2.54 log CFU) with the bland soap. Overall, lather time significantly influenced efficacy in one scenario, in which a 0.5-log greater reduction was observed after 20 s with bland soap compared with the baseline wash (P = 0.020). Water temperature as high as 38°C (100°F) and as low as 15°C (60°F) did not have a significant effect on the reduction of bacteria during hand washing; however, the energy usage differed between these temperatures. No significant differences were observed in mean log reductions experienced by men and women (both 2.08 log CFU; P = 0.988). A large part of the variability in the data was associated with the behaviors of the volunteers. Understanding what behaviors and human factors most influence hand washing may help researchers find techniques to optimize the effectiveness of hand washing.”

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CATEGORIZED UNDER: ha ha poop, told you so
  • OWilson

    The headline is a little misleading because the article refers to bacterial removal.

    Most mechanics will appreciate the fact that hot water can more easily remove grease and grime, or can it?

    If ever they could prove cold water could do the job, say, of dish washing, heavy laundering, as well as hand washing, we would see a revolution in energy use and a further drop in the price of fossil fuels!

    • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

      Anybody who uses a gravy separator know that solidified fat is not moved by common detergent. Heat it up to melt the fat and it comes right off.

    • AaronK

      I teach energy Education at a community action agency in Oregon. I will be checking into the data on this and seeing if the science pans out. As for your comment OWilson. Aside from “heavy laundering” we encourage all families to wash clothes in cold water. Detergent companies even push this fact. P&G pushed this at the Clinton Global Initiative on Sept. 21 2011. Since then nearly all liquid detergents have changed their surfactants and some have added enzymes to ensure they work just as well in cold water. In fact new washing machines get much of their efficiency rating by turning down the temperature. When you select hot it will temper the water down 30-40 degrees.

      • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

        Clinton Global Initiative” FNORD I’m an American. My laundry washes hot. I will not purchase social intent.

        “Fresh Start” solid laundry detergent omits excipients and inert fillers. it contains no solvent. It can be bought by the case for cheap/load. Less than a quarter cup does a drum-packed load of laundry to perfection.

        • AaronK

          I do not fault anyone who uses non-commercially available soaps. From what I remember Fresh Start was discontinued. After outcry the company replaced it with Start Fresh. This is a very similar product except they removed some dyes.

          I encourage everyone no matter what soap they use to try colder water. Even some “solid” low sudsing soaps will do great, in warm and cold water. If you are not happy with how well it cleaned, you simply run it again on a warmer setting. Some of my clients find that using a measuring cup with hot water in it helps to dissolve the dry mix. This is generally why solid powders tend not to work so well. They just don’t dissolve in the colder water.

          I have made my own soaps for years for the very reasons you mentioned. You can increase your savings by not paying for hot water (National Averages $0.55 for 30 gallons of hot water, 5 loads per week = $11.82/ month or $141.90/year).

          I have learned that most people will only take small steps toward a more sustainable future. Usually they will only do it if it saves them money. It is simple to get them to turn a dial on their washing machine to save cost and it reduces carbon emissions at the same time, BONUS. It is a leap to get them to change their detergent to something they have to special order, or make.

          • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

            “steps toward a more sustainable future.”
            Conservation: Somebody in the tenebrous future deserves to consume it, not you. Not them, either.

            I embrace primacy and dignity of the citizen and abhor egregious fallibility of the State, its leviathan bureaucracies, and its facile political sepsis. I believe in thermodynamics and engineering, in wasting what is cheap and abundant (the deserving!) to cherish what is dear and rare (the Severely Gifted). Mediocrity is a vice of the doomed. Eat the world.

            My way is better.

          • Cajun Exile


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          • OWilson

            Only for you and your world.

            But if you don’t conserve (leave it in the ground), what will those poor aliens use, when they leave their dying planet with all their resources used up, due to mad politicians who’s slogan is “drill, drill, drill”, and finally come to Earth to show us the error of our ways?

          • http://www.mazepath.com/uncleal/qz4.htm Uncle Al

            A few hundred Spanish psychotic felons versus 30 million New World indigenes: A horse, Damascus steel, and influenza beats pyramids, gods, and Neville Chamberlain.

          • Scott

            Its pretty funny that you pretend to be more righteous about the environment than a person who uses real soap and warm water while you type away on your cobalt and lithium powered device.

        • notearsinheaven

          these global warming idiots fly jets and tell us to turn off the water. MRSA is only killed by HOT water. Laundry also.

  • polistra24

    Ditto other comments. Maybe it’s true for bacteria, but it’s untrue for grease and general everyday dirt. Kitchen grease or car grease or even facial oil. Cold water does nothing.


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