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June 2020

[UPDATE] Hot or cold water - which kills more germs?

Written by Nathalie Leblond
Workplace Hygiene, Handwashing and Hand Hygiene

October 2017 feels like a long time ago, but that's when I wrote this original piece on which is better for washing your hands - hot or cold water. (Cape Town was just recovering from the Day Zero panic mindset and Capetonians were grateful to have any water at all, but Coronavirus has Day Zero paling into insignificance...)

None the less, with hand washing practices in the spotlight more than ever before, we thought now would be a good opportunity to update this blog post, and see whether Coronavirus has changed any of the thinking around which is best, or whether there is even a difference. 

Conventional wisdom holds that washing your hands with hot water kills more germs than washing them with cold water. According to the European Cleaning Journal “nearly 70 per cent of us believe hot water to be more effective than cold or warm water - despite having no evidence to back this up.”

So what do the experts think? 

Amanda R. Carrico, a research assistant professor at the Vanderbilt Institute for Energy and Environment in Tennessee, says "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."

And Unicef, on their page 'Everything you need to know about washing your hands to protect against Coronavirus, says "you can use any temperature of water to wash your hands. Cold water and warm water are equally effective at killing germs and viruses – as long as you use soap!"

And if you need further convincing, watch this short video in which the first thing an Infectious disease specialist says is "at a very practical level, it doesn't matter, as long as you are washing your hands with soap and water, that's all that matters".


The Warm Water Myth: 

The warm water myth seems to have originated because boiling water is often recommended as a means to make water safe for drinking. This is because at 100 degrees Celsius most pathogens are rendered harmless.

However, the average temperature for hand washing water is between 40 and 55 degrees Celsius. At the higher end of this spectrum some pathogens might die, but the amount of time your hands would need to be in the water would leave you with burns. 

Carrico said that after a review of the scientific literature, her team found no evidence that using hot water to wash hands kills bacteria. Carrico’s position was substantiated by research done at Rutgers University Brunswick  in which people were asked to wash hands in water of differing temperatures. Prof Donald Schaffner said: "People need to feel comfortable when they are washing their hands but as far as effectiveness [goes], this study shows us that the temperature of the water used did not matter".  Even water as cold as 4°C appeared to reduce bacteria if hands were scrubbed, rinsed, and dried properly. 

Technique matters!

Which brings me to the real point of this piece; it doesn't matter whether you use hot or cold water, as long as you wash your hands following proper hand washing techniques. These techniques include not only HOW you wash your hands,  but also for HOW LONG

And before you sigh, roll your eyes and say to yourself “of course I use the proper technique”, an 2013 article in Popular Science in claims that a staggering 95% of people don’t wash their hands for long enough to get rid of all the germs, and 23% don't even use soap. In 2016 Initial's "The Habits of Hygiene" report established that 84% of people claim to wash their hands after using the bathroom, but it’s really only half of that! We can really only hope that with good hand hygiene practices the single best weapon in the fight against Coronavirus, this statistic is now outdated and incorrect!

So how long is “long enough”? The CDC says you need to wash your hands—with soap!—for at least 20 seconds in order to kill disease-causing germs, but the sad reality is that most people only wash their hands for around 6 seconds.  And not to mention all those parts of the hands that most people forget to wash, such as their thumbs, the tops of their hands and between their fingers.  And last, but definitely not least, hand drying is important, as bacteria breeds faster on wet hands.  

For a reminder on the proper way to wash your hands, take a look at our expert demonstration or download our handy poster on hand washing techniques below.

Just remember that South Africa is still a water scarce country (even with all the winter rain in Cape Town), so always turn off the tap while you lather up, rather than leaving it running. You'll not only save water, but also electricity by not waiting for the water to get hot.

Coronavirus, Day Zero and Load shedding all defeated with one simple, 20 second behaviour... a girl can dream, right?

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Nathalie Leblond

Nathalie Leblond

I joined Rentokil Initial South Africa in 2004 as the PA to the MD, and after 6 months maternity leave I re-joined the Company in 2009 as the Marketing Co-ordinator for Rentokil. I'm now the Marketing Communication Manager for Rentokil Initial. I'm still terrified of cockroaches (Americana's only!) but the rest of the creepy crawlies we deal with don't really bug me (see what I did there?), so I guess I'm in the right industry! I am passionate about what we do here at Rentokil Initial and also write for our Hygiene Blog, which can be found at blog.initial.co.za, and our Ambius blog - https://www.ambius.co.za/blog. Life outside of Rentokil Initial mostly revolves around my daughter, who has just turned twelve, and my husband (who is a bit older). I love living in Cape Town and wouldn't trade living here for anywhere else in the world.

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