A humidifier producing fine steam vapor.

Flu season is in full swing, and public health officials are still urging anyone who hasn’t yet gotten a flu shot to do so. That's because the vaccine is the best way to protect yourself from the virus

Diligent hand-washing and staying home if you’re sick are two other important ways of preventing the flu and keeping it from spreading. But these strategies are not perfect, including the flu shot, which last year prevented about one in three flu illnesses. 

One additional flu-protection suggestion you may have heard about: humidifying the air around you. Some evidence linking flu activity with winter’s cold, dry weather conditions has led scientists to suggest that dry air helps the flu to spread while more humid air may make that harder. 

But can using a humidifier in your home or office really reduce your risk of catching the flu? Here, expert advice on whether you should add one of these devices to your flu-fighting arsenal.

The Connection Between Flu and Humidity

In temperate parts of the world, outbreaks of flu occur seasonally—in the U.S., beginning usually around the end of fall. A variety of factors likely contributes to that pattern, and the level of humidity may be one of them.

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For instance, in a 2017 study published in the journal Plos Computational Biology, researchers examined past flu seasons and found that predictions about flu incidence were more accurate when accounting for humidity.

Other experiments, using animals and cough-simulating mannequins, have found that flu virus is easily transmitted through the air when humidity is below about 40 or 50 percent, but less likely to be transmitted when the air is at or above 40 or 50 percent humidity.

There’s less evidence from real-life settings, but the research that exists is intriguing. In one study published in 2018 in the journal Plos One, researchers installed a commercial humidifier in two preschool classrooms, and compared them with two non-humidified classrooms. Over the course of several weeks of one flu season, they found that samples of air and objects the kids touched from the humidified rooms were less likely to be contaminated with the influenza A virus than those from the non-humidified classrooms. 

The researchers also tallied up school absences over the study period, and found that fewer kids from the humidified rooms were out sick with flu-like symptoms. But study author Jennifer Reiman, Ph.D., a member of the Citizen Science Faculty at Bard College, says that 2016, the winter the experiment was conducted, was a light flu year, and the overall number of absences due to flu was too low to draw any conclusions about whether humidifying the rooms really led to fewer illnesses.

Should You Humidify to Prevent Flu?

Despite the lack of conclusive evidence, using a humidifier is probably a good idea, says Seema Lakdawala, Ph.D., an assistant professor at University of Pittsburgh School of Medicine. 

Her laboratory research has found that while moderate humidity may not directly affect the flu virus itself, it does make virus particles heavier and faster to fall out of the air after a sick person has breathed, coughed, or sneezed them into a room. 

In winter, she says: “We’re in these really controlled indoor environments, where the air isn’t circulating, and we are breathing in what everyone else has breathed out.” So, keeping the air more humid may mean fewer particles of flu floating around, so you’re less likely to breathe them in later. (Of course, once flu lands on surfaces, you can pick the virus up via touch. But that’s where diligent hand-washing comes in.) 

Keeping home humidity between 40 and 60 percent is likely the sweet spot for reducing flu risks, according to Reiman. Going much more humid than that may backfire: Research in tropical climates, where flu season follows a different pattern than in most of the U.S., suggests that both very high and very low humidity help the virus to spread. 

Too much humidity can also encourage the growth of mold, bacteria, and dust mites, according to the Asthma and Allergy Foundation of America. (To keep air feeling comfortable but not damp, CR's experts typically recommend humidity levels between 30 and 50 percent.)

Our experts also recommend opting for a cool mist humidifier if you have children, because the tanks on warm mist devices contain water that’s hot enough to cause burns. Also, if you have a cold, warm mist can cause nasal passages to swell and actually make breathing more difficult, according to the Food and Drug Administration. 

Here, a few of our top-rated humidifiers. 

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CVS Health GUL540V1

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Air Innovations MH-701B

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Honeywell HUL520

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