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October 2017

Which kills more germs; hot or cold water?

Written by Nathalie Leblond
Cleanliness and Hygiene, Waterwise Hygiene Leave a Comment

Conventional wisdom holds that washing your hands with hot water kills more germs than washing them with cold water. 

Of course, residents of Cape Town at the moment are grateful for ANY water, but let’s not get diverted here. According to the European Cleaning Journalnearly 70% 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."

The warm water myth seems to have originated because boiling water is often recommended as a means to make water safe for drinking, as at 100 degrees celsius certain pathogens are rendered harmless. Of course, 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.

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”, and article in Popular Science claims that a staggering 95% of people don’t wash their hands for long enough to get rid of all the germs.

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 handwashing techniques below.

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Nathalie Leblond

Nathalie Leblond

Nathalie is the Category Manager at Rentokil Initial, and has worked in the hygiene and pest control industry for 12 years. Although after 12 years cockroaches still have the power to terrify her, she has learnt countless ways to defeat germs both in the workplace and at home. She is a passionate advocate for Global Handwash Day and the health benefits that can be derived from regular handwashing and hygiene practices. When not contributing to the Initial blog, Nathalie is writing press releases for sister businesses, Rentokil and Ambius. You can find her on LinkedIn.

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