Study led by Richard Zare details how low humidity could be a boon for viruses

New Stanford research adds to evidence that the seasonality of respiratory illnesses, like COVID-19 or the flu, can be linked to indoor humidity levels. The study, which found that ventilation reduces the presence of naturally occurring disinfectant compounds in airborne microdroplets, could add another dimension to public health approaches to seasonal viruses.

“Indoor relative humidity of 40% to 60% has long been recommended by experts, and now this research points to a significant benefit: humidity in this range naturally creates anti-viral compounds in the air’s microdroplets,” said Richard Zare, the Marguerite Blake Wilbur Professor in Natural Science and a professor of chemistry in the Stanford School of Humanities and Sciences. Zare is the senior author of a paper about this work, published March 11 in Proceedings of the National Academy of Sciences. “This could lead to controlling indoor relative humidity in a way that could radically alter how we combat airborne viral infections,” Zare added.

Previous research led by Zare revealed that hydrogen peroxide, a common disinfectant, can spontaneously form in water microdroplets. Now, the researchers have discovered that, as humidity increases, so does the concentration of hydrogen peroxide and other naturally occurring disinfectant agents in the air. This new finding suggests that ventilation aimed at preventing the spread of disease – which tends to dry air out – could be counterproductive, and reveals a possible mechanism for the increased number of cases of airborne viruses during the winter months when heating and ventilation are used more often. The study also highlights the possibly beneficial effects of increased humidity for reducing the spread of airborne viruses.

Read the press release in the Stanford News.