It takes a good 20 seconds of vigorous hand-washing with soap to be sure the virus lifts off the skin, and a thorough rinsing to flush it away. Nothing works better than that, says Dr. Jeffrey A. Linder, professor and chief of the division of general internal medicine and geriatrics at Northwestern University’s Feinberg School of Medicine. Hand sanitizer, he says, “is better if it’s in lieu of doing nothing.”
A recent study in the journal mSphere, from the American Society for Microbiology, compared soap and water to hand sanitizer containing 80% alcohol on the flu virus in mucus. It found that soap and water thoroughly removed the virus after 30 seconds in both wet and dry mucus. It took hand sanitizer the same amount of time when the mucus had dried for 40 minutes, but up to four minutes when it was still wet.
Hand sanitizer products work differently than soap and water. “The alcohol in the sanitizer basically breaks up the virus,” Linder says, by destroying the outer membrane of the virus cell, effectively killing it or making it unable to reproduce. But there has to be enough alcohol in the product to be effective, so be sure to check hand sanitizer labels carefully. Effectiveness drops off significantly when the alcohol level is below the minimum. Higher levels are only marginally better.
Also use a generous amount of hand sanitizer, LeRoy advises, and rub it into your skin for 20 seconds, until it evaporates. “Remember that 20-second rule,” he says, with both hand sanitizer and soap and water. (Though the more recent study looked at 30-second intervals, most experts still recommend a minimum of 20 seconds.) To ensure hand sanitizer is effective against germs, the CDC warns against rinsing or wiping off hand sanitizer before it’s completely dry.