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Water For Hand-Washing: How Hot Is Hot Enough?

Health experts urge hand-washing for 20 seconds to help stem the spread of the coronavirus. But just how hot does that water need to be?

Whether you scrub your hands to "Happy Birthday" or the alphabet song or Lady Macbeth's "Out, damned spot" speech, you might wonder if that tepid water is really doing the job.

Well, fear not. Water hot enough to kill germs — starting at 140 to 165 degrees Fahrenheit (60-74 C) — would scald you, which is why hot water supply codes usually cap faucet water at 120 degrees.

Will Humble, executive director of the Arizona Public Health Association and former director of the Arizona Department of Health Services, explained the real reason the food code requires hot and cold taps.

"Hot water doesn't do any better than cold water. It's just that warm water encourages people to wash their hands longer, and so therefore it's more effective," he said.

As for soaps, a research survey has shown regular soap performs as well as antibacterial soap in reducing respiratory illnesses.

"I'm not trying to throw stones at antibacterial soap. I'm just telling folks, just because you're using antibacterial soap doesn't mean you can shortchange your hand-washing and cut it off earlier," said Humble.

Why the 20-second rule? Research has shown significantly fewer germs remain on hands after 20 seconds of scrubbing than after just 15, but found no appreciable difference among subjects who washed their hands longer than 20.

If soap and water are not available, the Centers for Disease Control and Prevention recommends using an alcohol-based hand sanitizer with at least 60% alcohol.

→  Read The Latest News On The Coronavirus Disease  

Nicholas Gerbis was a senior field correspondent for KJZZ from 2016 to 2024.