This higher level of humidity in inhaled air could help explain why wearing masks has been linked to lower disease severity in people infected with SARS-CoV-2, because hydration of the respiratory tract is known to benefit the immune system, according to the paper published in the Biophysical Journal.

 

"We found that face masks strongly increase the humidity in inhaled air and propose that the resulting hydration of the respiratory tract could be responsible for the documented finding that links lower Covid-19 disease severity to wearing a mask," said lead author Adriaan Bax from National Institute of Diabetes and Digestive and Kidney Diseases.

 

"High levels of humidity have been shown to mitigate severity of the flu, and it may be applicable to severity of Covid-19 through a similar mechanism," Bax added.

 

High levels of humidity can limit the spread of a virus to the lungs by promoting mucociliary clearance (MCC), a defence mechanism that removes mucus and potentially harmful particles within the mucus from the lungs, the researchers said.

 

For the study, the team tested four common types of masks -- an N95 mask, a three-ply disposable surgical mask, a two-ply cotton-polyester mask and a heavy cotton mask.

 

The researchers measured the level of humidity by having a volunteer breathe into a sealed steel box.

 

The results showed that all four masks increased the level of humidity of inhaled air, but to varying degrees. At lower temperatures, the humidifying effects of all masks greatly increased. At all temperatures, the thick cotton mask led to the most increased level of humidity.