While scientists have long known that air pollution poses a threat to lung health, a recent study led by Johns Hopkins researchers points to a new culprit: dry air.

In a recent, cross-institutional study partially funded by the National Institutes of Health (NIH), the team found that healthy human airways are at higher risk for dehydration and inflammation when exposed to air depleted of moisture. Inflammation in human airways is associated with such conditions as asthma, allergic rhinitis and chronic cough.

“Air dryness is as critical to air quality as air dirtiness, and managing the hydration of our airways is as essential as managing their cleanliness,” says lead author David Edwards, adjunct professor of medicine at the Johns Hopkins University School of Medicine. “Our findings suggest that all mucosa exposed to the atmosphere, including ocular mucosa, are at risk in dehydrating atmospheres.”

Researchers say that as the earth’s atmosphere heats up, with relative humidity staying mostly the same, a property of the atmosphere called vapor pressure deficit (VPD) increases at a rapid rate. VPD is a measure of how “thirsty” for water air can be. The higher VPD becomes, the greater the evaporation rate of water, thus dehydrating planetary ecosystems.

Based on mathematical predictions and experiments, researchers now explain that higher VPD can dehydrate upper airways and trigger the body’s inflammatory and immune response. They also say that such dehydration and inflammation can be exacerbated by mouth breathing (rates of which are also increasing) and more exposure to air-conditioned and heated indoor air. Their full report is published in Communications Earth & Environment.

“This manuscript is a game changer for medicine, as human mucosa dehydration is currently a critical threat to human health, which will only increase as global warming continues,” says study co-author Justin Hanes, the Lewis J. Ort Professor of Ophthalmology at the Wilmer Eye Institute, Johns Hopkins Medicine. “Without a solution, human mucosa will become drier over the years, leading to increased chronic inflammation and associated afflictions.”