How hot should the water be?

“Hot water for handwashing has not been proved to remove germs better than cold water.”

That’s the conclusion of The Claim column in tomorrow’s N.Y. Times science section.

We’ve been saying for a couple of years that water temperature is not a critical factor -- water hot enough to kill dangerous bacteria and viruses would scald hands -- so use whatever is comfortable. Warmer water may be better at removing oils and stuff, but not the things that make people sick.

The Times story says,

In its medical literature, the Food and Drug Administration states that hot water comfortable enough for washing hands is not hot enough to kill bacteria, but is more effective than cold water because it removes oils from the hand that can harbor bacteria.

But in a 2005 report in the Journal of Occupational and Environmental Medicine, scientists with the Joint Bank Group/Fund Health Services Department pointed out that in studies in which subjects had their hands contaminated, and then were instructed to wash and rinse with soap for 25 seconds using water with temperatures ranging from 40 degrees Fahrenheit to 120 degrees, the various temperatures had “no effect on transient or resident bacterial reduction.”

They found no evidence that hot water had any benefit, and noted that it might increase the “irritant capacity” of some soaps, causing contact dermatitis.

“Temperature of water used for hand washing should not be guided by antibacterial effects but comfort,” they wrote, “which is in the tepid to warm temperature range. The usage of tepid water instead of hot water also has economic benefits.”