COVID-19 Resource Center

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Disclosures: Bax, Courtney and Rodgers are NIH employees.
February 15, 2021
1 min read

Humidity in face masks may offer additional protection from COVID-19

Disclosures: Bax, Courtney and Rodgers are NIH employees.
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The humidity created inside face masks may offer additional protection against COVID-19, according to NIH researchers.

“We show that face masks strongly increase the effective humidity of inhaled air, thereby promoting hydration of the respiratory epithelium which is known to be beneficial to the immune system,” NIH investigators Joseph M. Courtney, PhD, and Adriaan Bax, PhD, wrote in Biophysical Journal. “Increased humidity of inspired air could be an alternate explanation for the now well-established link between mask wearing and lower disease severity.”

NIH breathing box
In a recent experimental study, masked participants breathed into a sealed box to demonstrate how humidity can protect against SARS-CoV-2.
Credit: National Institute of Diabetes and Digestive and Kidney Diseases, NIH

Courtney and Bax tested N95, three-ply disposable, two-ply cotton-polyester and heavy cotton masks. They had volunteers breathe into a steel sealed box to test the effects of humidity on the virus. Humidity can limit viral spread to the lungs by influencing mucociliary clearance, a mechanism that removes mucus and harmful particles contained within it, the NIH noted in a press release.

The researchers took measurements at three temperatures from 46°F to 98°F. When volunteers wore a mask, humidity buildup within the box significantly dropped. All four types of masks tested increased the humidity level of inhaled air by varying degrees. At low temperatures, the humidifying effects of masks increased, and the thick cotton mask showed the most increased humidity levels across all temperatures — “about double that of a surgical mask,” Courtney and Bax wrote.

“Even as more people nationwide begin to get vaccinated, we must remain vigilant about doing our part to prevent the spread of the coronavirus that causes COVID-19,” Griffin P. Rodgers, MD, MACP, who heads the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases, which supported the research, said in a press release. “This research supports the importance of mask wearing as a simple, yet effective, way to protect the people around us and to protect ourselves from respiratory infection, especially during these winter months, when susceptibility to these viruses increases.”

CDC researchers recently reported that wearing two masks can increase protection from SARS-CoV-2, as can modifying surgical masks by knotting the ear loops near the mask’s edges and tucking in the extra material.


Press Release