Researchers ask WHO to adopt guidelines for humidity in public buildings

BOSTON — A group of global scientists and researchers led by doctors from Harvard and Yale have come together to launch a petition calling on the World Health Organization to provide guidelines on the recommended levels of humidity in public buildings. The doctors say by keeping the “relative humidity” level in buildings within recommended guidelines, it would protect public health.

We pay a lot of attention to the indoor air temperature in our homes and offices, but Dr. Stephanie Taylor, an infection control consultant for Harvard Medical School and CEO of Taylor Healthcare Consulting, says we don’t pay enough attention to the relative humidity levels in the public buildings we spend time in.

“Businesses, homes, schools and hospitals, in my opinion, should all be maintained with the relative humidity level between 40 and 60 percent,” said Taylor, whose research suggests that when inside humidity is low, infection rates increase.

Akiko Iwasaki, professor of immunobiology at Yale School of Medicine, said people tend to get sicker in the winter when outside air is cold and we “import that air inside the home to 70 degrees,” and lower the relative humidity inside to between 20 to 40%.

“That’s actually a very low humidity and dry air, and that promotes the transmission of the virus and the stability of the virus,” she said.

The kind of microbes that cause viruses and airborne bacteria tend to survive longer in dry air. Low humidity, the researchers say, also impairs the immune system’s ability to fight a virus.

Iwasaki said researchers in her lab have been studying the environmental impact on the immune system, including the role of temperature and humidity on respiratory infections.

Taylor and Iwasaki have launched a petition calling on the WHO to review their research, and establish a minimum indoor relative humidity level of 40% -- a threshold they say many public buildings drop below every winter.

New buildings could be required to have humidification systems installed with HVAC equipment, but older buildings would have to be retrofitted.

“Right now, building managers focus on an upper limit of relative humidity but neglect the lower limit,” Taylor said.

"Obviously there are expenses associated with it, but if this minimum level of relative humidity at 40% were actually a best practice or mandated, I think we would find a way to prioritize our budgets to incorporate humidification in buildings. We see this being done in museums, in animal research laboratories, and in the NASA space station.”

Taylor said adopting the standards suggested in their petition wouldn’t totally eliminate viruses like common colds or coronaviruses, but would make it easier to live with them.

For a short-term fix to improve the humidity level in your house, the researchers recommend buying an inexpensive hygrometer to measure the relative humidity level and adding a portable humidifier to increase the humidity.

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