Think twice before using hand sanitizer to fight the flu

Trying to protect yourself from the flu this year? Use something other than hand sanitizer.

There’s common belief that hand sanitizer kills germs instantly, cleaning up messy hands with a quick squeeze in seconds. While hand sanitizer does kill germs — both good and bad — it won’t do much to kill cold and flu bugs, according to a new study.

That’s because your fingers still have mucus on them, which isn’t immediately thwarted when applying hand sanitizing products, according to research published in the journal mSphere. Japanese researchers dabbed participants with IAV-infected wet mucus onto their fingertips, finding that ethanol-based products didn’t kill the virus even when with it left on their fingers for two minutes. It took a total of four minutes for the virus to be deactivated, according to the study.

“The physical properties of mucus protect the virus from inactivation,” said Ryohei Hirose, Ph.D., MD., a physician and molecular gastroenterologist at Kyoto Prefectural University of Medicine in Japan, in a press release. “Until the mucus has completely dried, infectious IAV can remain on the hands and fingers, even after appropriate antiseptic hand rubbing.”

It’s all about the dryness of the mucus

Past studies have shown that ethanol-based disinfectants can be effective against IAV, but as researchers noted, most tests using disinfectants were on mucus that was already deemed dead. For this study, they found that with fully dried mucus, hand rubbing disinfectant killed the virus within half a minute.

The CDC advises washing hands with soap and water is the best way to reduce microbes in most situations, but if those are not available, an alcohol-based hand sanitizer with at least 60% alcohol is your best bet.

Researchers found that the CDC is right — when washing your hands with antiseptic soap, the flu virus was deactivated within 30 seconds, whether the mucus remained wet or dried.

A study from 2018 found that some bacteria that hand sanitizers aim to kill became “more tolerant” to alcohol-based products, which essentially means the bacteria can survive for longer time lengths.

The study was conducted by Ryohei Hirose, a physician and molecular gastroenterologist at Kyoto Prefectural University of Medicine and Takaaki Nakaya, PhD., a researcher at Kyoto Prefectural University of Medicine.