Dear Dr. Roach: In your recent answer regarding proper hand-washing, you stated, “These germs are not killed by the gel and need to be washed off the hands with warm, soapy water for at least 20 seconds.”

My question is why “warm” water is necessary. For the temperature of the water to have any therapeutic effect, it would have to be too hot to tolerate. The procedure of washing one’s hands with water and soap, mechanically, removes germs. The temperature is immaterial. Aside from comfort, is there any reason to use warm water?

I would hate to think that someone would forgo washing because only cold water was available. — D.G.

Answer: Warm water is better able to dissolve particles on the hands. The temperature is not designed to kill the bacteria.

However, it turns out that washing your hands with any temperature water (cold, warm or hot) is just as effective, at least in terms of getting rid of bacteria. Washing in too-hot water can cause irritation to the skin, but you can use whatever temperature you like, for at least 20 seconds. I thank D.G. for questioning conventional wisdom.