BehindTheMedspeak: Does water temperature matter when you wash your hands?

Long story short: No.

Anahad O'Connor's "Really?" column in yesterday's New York Times Science section had the back story; it follows.

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The Claim: Always Wash Your Hands With Hot Water, Not Cold.

The Facts: With swine flu sweeping across the country, health officials are reminding Americans to wash their hands often to reduce the spread of the disease.

Soap and warm water have long been said to prevent the spread of infections, but is warm or hot water really more effective than cold?

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.”

The Bottom Line: Hot water for hand washing has not been proved to remove germs better than cold water.