Increasing indoor humidity can protect against the flu: researchers

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TORONTO — In addition to handwashing and vaccinations, Canadians may want to consider investing in a humidifier this winter to keep the flu at bay, according to researchers.

As the temperature drops so does the moisture in the air, which can have harmful effects on human health.

"Dry indoor air is bad for humans," Dr. Stephanie Taylor, a Harvard Medical School lecturer, pediatric oncologist, and molecular biologist, told CTV News. "Dry indoor air fosters the presence of more infectious bacteria and viruses."

According to scientists, dry air allows viral particles to survive for longer periods and hinders the ability of our noses and lungs to rid themselves of viruses. On top of that, dry air can obstruct the immune system's interferons, which are proteins that help fight off infections.

"We found the low humidity impairs the expressions of these interferon and interferon-stimulating genes," Akiko Iwasaki, an immunobiologist at Yale University, said.

It's still unclear why this happens and Iwasaki said it remains a topic for future research.

"How does inhalation of low-humidity air impact immune defence against the virus?" she said.

In one study, published in the journal PLOS ONE, the cyclical reduction of humidity was associated with influenza outbreaks in temperate climates. The researchers found that when children were in properly humidified classrooms, flu-related absenteeism dropped by 66 per cent.

"We show that humidification can reduce the amount of influenza present within samples from preschool classrooms and that there were fewer infectious samples compared to non-humidified rooms," the study's authors wrote.

The key, however, is maintaining the right amount of moisture in the air because too much humidity can also be harmful to human health.

"Humidity is one of those Goldilocks things. You don't want too much and you don't want too little. So if we keep our indoor environment too moist we favour the spread of moulds and the growth of mould in doors and obviously we don't want that," Dr. Ray Copes, chief of environmental and occupational health at Public Health Ontario, said.

"If we have it too low, some evidence that that may increase a transmission of viruses and also creates symptoms like dry, itchy skin and dry eyes."

Although there are varying recommendations, Copes said people should aim for 40 to 60 per cent relative indoor humidity.

Taylor also agreed that keeping indoor humidity between 40 to 60 per cent is "very protective to human beings."

In fact, with proper indoor humidification, Taylor said she believes influenza rates could be dramatically decreased.

"Based on the research, we could reduce influenza by 60 per cent and I can say that with confidence," she said.

Taylor recommended investing in a larger space humidifier, or if that's not in the budget, a smaller unit to put in the bedroom or living room.

"Put it wherever you spend time and try to maintain your humidity between 40 and 60 per cent," she said. "I can guarantee you will feel better and I don't usually make claims like that."