A mother watches as her two children wash their hands a the sink.

Washing your hands under running water may be a better way to stop the spread of infections than using a hand sanitizer. In a new study published in the journal mSphere, researchers found that hand-washing removed the flu virus from hands more quickly and more effectively than using a dab of alcohol-based hand sanitizer.

The new study builds on previous research suggesting that hand-washing is superior for infection control, but the real-world implications of the new findings are limited. The study compared putting hand sanitizer on (without rubbing it in) to using running water (while rubbing hands together). It didn't factor in how rubbing your hands together while using sanitizer or using soap while washing may affect the results, says the study's author, Ryohei Hirose, M.D., Ph.D., at the Kyoto Prefectural University of Medicine in Japan.

Proper hand hygiene is important for preventing the transmission of respiratory infections like colds and flu, which are easily caught if you touch an infected surface and then touch your mouth or nose. 

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As with previous studies, the new research found that using hand sanitizer can remove the flu virus, but it took far longer than hand-washing did. One of the main reasons, the researchers found, is that the mucus from the mouth and nose—which contains the flu virus if you’re infected—makes it difficult for the alcohol in hand sanitizers to penetrate.

“We had predicted that the virus in mucus would be somewhat resistant to alcohol disinfectants,” says Hirose. But it seemed to shield the flu virus from the hand sanitizer even more than expected.

Still, don’t toss out your bottle of hand sanitizer just yet. Here’s what you need to know about this study, how to keep your hands germ-free, and how to protect yourself from respiratory viruses as we head into the cold and flu season.

What the Study Found

In hospitals and other healthcare settings—where workers must clean their hands many times a day—using hand sanitizer can be a quicker and easier than washing. And it’s advised in some instances, such as before and after contact with a patient, when a worker's hands aren’t visibly dirty.

In this study, researchers sought to shed light on when hand sanitizers are most effective, and whether recommendations for healthcare workers on using them could be improved. Hirose says the findings are useful for other people, too.

To determine which hand-cleansing method was best at killing the flu virus, the researchers exposed samples of flu virus in saline and flu virus in mucus to 80 percent alcohol hand sanitizer. (Earlier studies tended to test hand sanitizer on flu samples that were in thin, watery fluid only, so these researchers wanted to also test mucus, because it’s thicker and what people encounter in real life.) It took about 30 seconds for the sanitizer to eliminate all the flu virus in the saline samples, but more than 4 minutes for the sanitizer to get rid of flu in the mucus samples.

Next, the researchers tested the effects of hand sanitizer and hand-washing on people’s hands. The scientists applied flu-infected mucus to the fingertips of 10 volunteers. When the mucus was first allowed to dry completely (for 40 minutes), the hand sanitizer eradicated the flu virus within 30 seconds. But when the hand sanitizer was applied while the mucus was still wet, it took about 4 minutes for the flu virus to be completely eliminated.

In contrast, hand-washing completely removed the flu virus after 30 seconds, whether the mucus was wet or dry. This held true even though the volunteers used no soap while hand-washing. Simply running their hands under water and rubbing them together was fast and effective—a surprise to the researchers, Hirose says.

Hirose points out that hand sanitizers may work more quickly than this study suggests, because the tests didn’t account for how rubbing your hands together—which people tend to do with hand sanitizer in real life—might speed up the distribution of the alcohol across your skin. Hirose says his team is working to clarify how much rubbing might improve hand sanitizer’s effectiveness.

What This Study Means for You

For people who don’t need to clean their hands numerous times during the workday, as healthcare workers do, the CDC recommends washing them with soap and water if it’s available and using hand sanitizer if it’s not. The results of this study support that recommendation, says Allison Aiello, Ph.D., a professor of epidemiology at the University of North Carolina at Chapel Hill's Gillings School of Global Public Health, who wasn’t involved in the new study. 

Despite the positive results of washing without soap in the study, it’s really best to suds up, experts say. Other studies have shown that washing with soap removes germs more effectively than washing with water alone, Aiello says. 

What to Do to Prevent the Flu

Use proper hand-washing technique. The CDC recommends scrubbing with soap and water for at least 20 seconds. Be sure to clean the back of your hands, between your fingers, and under your fingernails. 

Use hand sanitizer (with at least 60 percent alcohol) only if a sink isn't available. But keep in mind that while hand sanitizers have some effect on cold and flu viruses, they don’t eliminate all types of germs from hands. For instance, they don’t kill Clostridium difficile, a "superbug" that causes severe diarrhea that can occur as a side effect of antibiotics. Hand sanitizers also don’t do a good job of cleaning visibly dirty hands.

While regular hand-washing is crucial, it’s important to take other steps, too. That’s because the flu is also commonly spread through the air. “You could be in a room with someone, and they could be coughing, and those small particles that they are coughing out, you can breathe into your lungs,” Aiello says. “It’s really not all about hands.”

So try to limit your contact with people you know are sick. And if you do get sick, stay home to avoid infecting others. 

But remember, the No. 1 way to reduce your risk of catching the flu is by getting the flu vaccine. The CDC recommends vaccination before the end of October so that you’re protected by the time the season ramps up.