Duration is more relevant

Water temperature when washing hands doesn’t matter

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Whether you wash your hands with cold or warm water after using the toilet makes no difference. It is the duration of the washing process and the use of soap that make the most difference. 

• Main results of a new study*: Washing hands with cold water for ten seconds resulted in a decrease in germ concentration of 1.93 powers of ten (two powers of ten: minus 99 percent). There was no statistical difference to using water at 40 degrees Celsius (minus 2.01 powers of ten).

• The results were similar for washing for 20 seconds (cold water minus 2.23 powers of ten; warm water minus 2.39 powers of ten). However, the stronger effect of washing hands for longer was already statistically significant compared to just ten seconds.

One minute helps best 
However, all test arrangements were statistically inferior to washing hands with soap for one minute. The number of germs on the fingers was reduced by 2.68 powers of ten.

Hand washing for ten or 20 seconds with cold (...) or warm water "was significantly worse than the one-minute reference procedure of hand washing with Sapo kalinus (potassium soap; note), but there were no significant differences between the use of cold or warm water in a pairwise comparison for both times.

Duration has an effect on germ reduction
However, duration appears to have an effect on germ reduction, as the differences between hand rinsing times were significant for both temperatures," the scientists said.

*Romana Kordasiewicz-Stingler from MedUni Vienna's Institute of Hygiene and Applied Immunology and co-authors in a publication by the German Society for General and Hospital Hygiene (DGKH; doi: 10.3205/dgkh000527)