Key takeaways

Hand sanitizer can kill the flu virus but is less effective on the virus trapped in wet mucus, taking up to four minutes, compared to 30 seconds in saline solution and eight seconds in dried mucus.
Handwashing without soap can remove the flu virus in 30 seconds, even from wet mucus, highlighting the effectiveness of proper hand hygiene over the type of cleansing agent used.
The mechanical action of rubbing hands together when using hand sanitizer is crucial for its effectiveness, emphasizing the importance of technique and the sanitizer’s chemical action.
For optimal flu protection, hand sanitizer should include at least 60% ethanol alcohol and a thorough rubbing method, while handwashing should involve at least 20 seconds of scrubbing with soap and water.

Ever since the COVID-19 pandemic started, you’ll see hand sanitizer just about everywhere: banks, grocery store checkout lines, the post office, and public bathrooms. We’ve been told it’s the second best way to wash hands if good ‘ol soap and water isn’t available. So is hand sanitizer a formidable foe to the flu virus? Or is old-fashioned soap and water best? Well, according to 2019 research, it’s complicated.

Does hand sanitizer kill the flu virus?

When the flu virus is trapped in wet mucus, it can remain infectious for up to four minutes after exposure to hand sanitizer—in other words, much longer than you might have guessed. This is what a recent study found when dabbing wet mucus droplets containing the influenza A virus onto the fingertips of brave volunteers.

When the flu virus was suspended in a saline solution, the disinfectant killed the virus in 30 seconds. When applied to dried flu germs, hand sanitizer killed the virus in just eight seconds.

The researchers, from Kyoto Prefectural University of Medicine, reason that thick, goopy mucus acts as a shield around the virus, preventing the hand sanitizer from fully penetrating it. Saline—not goopy or thick—doesn’t limit the sanitizer’s ability to get into the virus and do its work. Ditto for dried mucus. That’s why the time to eradicate the virus varies so widely.

Not everyone exposed to the flu virus has the luxury of choosing the way the virus ends up on their hands—in mucus, saline, or dried. So it’s important to know how long it takes for hand sanitizer to work properly. Otherwise, you could risk infecting yourself or spreading the virus to others.

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Does handwashing kill the flu?

According to the study, handwashing—even without soap and even when the infected mucus was wet—was, indeed, very effective in removing the flu virus. It eliminated it in just 30 seconds. The only problem is that most people don’t wash their hands for nearly that long, and in many situations soap and running water simply aren’t available. In those cases, is hand sanitizer useless?

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It’s all about proper hand hygiene

No matter the method you choose—sanitizer or soap and water—the key is how well and how long you cleanse. Not everyone agrees with the new findings, especially because the researchers didn’t study how hand sanitizer works when it’s rubbed into the skin, only when it was dabbed onto fingers.

“The fight wasn’t fair,” says Carl Fichtenbaum, MD, a professor of medicine in the department of internal medicine, division of infectious diseases at the University of Cincinnati College of Medicine. “Hand sanitizers are always used with a rubbing motion—you have to rub it into your hands to get it to evaporate and dissolve. That’s the real experiment that needed to be done. Hand rubbing is the critical part of all this.”

Michael Chang, M.D., an infectious disease pediatrician and an assistant professor of pediatrics at McGovern Medical School at UTHealth in Houston, concurs. “The probability that you would squirt hand sanitizer onto your hand and let it sit there is low,” Dr. Chang says. “No one uses hand sanitizer that way.”

Both Drs. Fichtenbaum and Chang noted that it’s more than the chemical action of hand sanitizer that makes it effective—it’s also the mechanical action of rubbing hands together. “I think if the researchers had looked at rubbing the hand sanitizer into the hands and fingers, it might have been as effective as handwashing in killing the virus,” said Dr. Fichtenbaum.

The researchers acknowledged the limitations of their study and are looking at expanding their research to include hand rubbing.

“We are verifying the scientific significance of the act of hand rubbing in order to propose the best hand-rubbing regimen,” said Ryohei Hirose, the study’s lead author. “Hand rubbing is expected to contribute significantly to the increase in the rate of ethanol concentration in infectious mucus due to an increase in convection.”

When (and how) to best use hand sanitizer

Experts say the best protection from the flu is a flu shot, then practicing proper hand hygiene. Meaning, make sure you’re using an effective cleanser and applying it the right way.

If you’re using a hand sanitizer, the Centers for Disease Control and Prevention (CDC) recommends these dos and don’ts.

Do use a hand sanitizer with at least 60% ethanol alcohol.
Do apply the sanitizer to the palm of your hand (read the product’s directions for the right amount—usually a squirt or two) and rub all over the surfaces of both hands until sanitizer is dry (about 20-30 seconds).
Do rub sanitizer in between the spaces of fingers and even up under nails.
Don’t use a hand sanitizer if hands are visibly dirty or greasy, two things that make it tougher for the sanitizer to penetrate germs.

If you’re using soap and water, the CDC recommends these steps:

Wet your hands with clean running water—hot or cold.
Apply soap. It doesn’t have to be antibacterial.
Scrub your palms, back of hands up to wrists, between fingers and under nails for at least 20 seconds. That’s about the time it takes to hum the “Happy Birthday” song twice.
Rinse your hands well.
Dry with a clean towel, or air dry.

No matter which method you choose, if you follow these steps, you’re more likely to avoid a cold, the flu, or COVID-19.