Consumer Reports: Dry Air Encourages Flu Virus


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Keeping the air moist during home heating season helps ease dry skin, relieve itchy eyes and throats and reduce static electricity. Now, here’s another reason to consider using a humidifier or putting out pans of water near heating units to increase the moisture in your home: It may help curb the flu. How’s that? Scientific research has shown a link between the spread of the flu and low humidity so boosting the humidity in your home may hinder the ability of flu germs to spread.

One just-released white paper, for example, suggests that homes with 40% to 60% humidity are likely to have fewer flu viruses lingering in the air or on common surfaces, such as computer keyboards, TV remotes or even the kitchen sink than in homes where the humidity is low, say around 20%.

“While the typical flu virus can survive on surfaces and in the air for up to 24 hours, the survival time in a more humid environment is markedly lower,” said Jim McDevitt, Ph.D., a certified industrial hygienist and instructor at the Harvard School of Public Health.

We must note here that the white paper was sponsored by Kaz, which makes Vicks brand humidifiers. Even so, the conclusion is similar to another study published earlier this year in the Proceedings of the National Academy of Sciences. That study, by Oregon researchers, found a significant correlation between “absolute” humidity (the actual amount of water in the air, irrespective of temperature) and the influenza virus survival and transmission. When absolute humidity is low—as in the peak flu months of January and February—the virus appears to survive longer and transmission rates increase. By contrast, the absolute humidity in the summer months is higher.

For years, scientists have theorized that the flu spreads in winter because people spend more time indoors so the virus is more easily transmitted. But the Oregon researchers suggest that absolute humidity is the key.

“In some areas of the country, a typical summer day can have four times as much water vapor as a typical winter day—a difference that exists both indoors and outdoors,” said lead author Jeffrey Shaman, Ph.D., an atmospheric scientist at Oregon State University. “Consequently, outbreaks of influenza typically occur in winter when low absolute humidity conditions strongly favor influenza survival and transmission.”

As a result, the study urges that indoor humidity be increased, particularly in areas where people are at high-risk for complications from the flu such as nursing homes and emergency rooms. Such action “may help decrease the spread and the toll of influenza during influenza season.”

To improve moisture levels at home, keep your thermostat set low—68° F (20° C)—and consider using a humidifier to maintain a humidity level between 30% and 50%.

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