When you wash with running water, the rubbing action of your hands removes the mucus surrounding the virus and washes the virus down the drain.

Washing your hands under running water — even without soap — is more effective at stopping the spread of flu germs than using ethanol-based hand sanitizers, according to Japanese researchers.

The reason: When wet mucus surrounds the virus, it acts as a protective hydrogel, keeping the disinfectant from reaching and killing the germs. But when you wash with running water, the rubbing action of your hands (if you do it thoroughly) removes the mucus and washes the virus down the drain.

The authors of the study, which was published earlier this week in the journal mSphere, say they were somewhat surprised by their results. Previous studies have suggested ethanol-based sanitizers are effective against flu viruses.

“We had predicted that the virus in mucus would be somewhat resistant to alcohol disinfectants,” said Dr. Ryohei Hirose, the study’s lead author and a molecular gastroenterologist at Kyoto Profectural University of Medicine, in an interview with Healthline. “However, we found that the protective effect of mucus is stronger than expected and there may be room for improvement in current hand hygiene guidelines.”

How to wash your hands

The publication of this study comes at the start of a new flu season. Its findings are a good reminder that keeping your hands clean is one of the most effective preventive steps you can take to avoid both “catching” the flu and spreading it to others. (The most effective step is to get this year’s flu vaccine.)

The Centers for Disease Control and Prevention (CDC) recommends that you follow these five simple steps when washing your hands:

• Wet your hands with clean, running water (warm or cold), turn off the tap, and apply soap.

• Lather your hands by rubbing them together with the soap. Be sure to lather the backs of your hands, between your fingers, and under your nails.

• Scrub your hands for at least 20 seconds. Need a timer? Hum the “Happy Birthday” song from beginning to end twice.

• Rinse your hands well under clean, running water.

• Dry your hands using a clean towel or air dry them.

And if you don’t have clean running water? Then, yes, use a hand sanitizer, the agency says. Make sure you rub it all over your hands, and keep rubbing until your hands are dry.