Want to kill some germs and disinfect your hands? Use hot water. Right? Using cold water with some regular soap may just be as effective according to researchers at Vanderbilt University.

While it may be more comfortable, and comforting to wash your hands with hot water, it may not make that much of a difference compared to some cold water. Amanda R. Carrico, a research assistant professor at the Vanderbilt Institute for Energy and Environment, explained to National Geographic:
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.
It is that reason that the Centers for Disease Control or the World Health Organization actually specify water temperature in their handwashing guidelines. They do suggest scrubbing with soap for at least 20 seconds but the key is to wash well and wash often. You don't even have to use hot water.

Most people would prefer to use warm water by all means, but researchers do point you should wash your hands at a comfortable temperature. Read more in the report below:

[The International Journal of Consumer Studies (May 2013, Vol. 34, Issue 4) via National Geographic and Tested Image via Katherine Johnson]