It’s not just the mask, it’s the humidity created inside the mask that helps protect against severe COVID-19, a recent study by National Institutes of Health (NIH) researchers suggests.
The use of cloth masks has been linked with decreased disease severity, which is surprising considering such masks aren’t good at filtering out the smallest aerosol particles that can reach the lower respiratory tract, the researchers wrote.
They tested 4 types of masks: an N95 respirator, a 3-ply disposable surgical mask, a 2-ply cotton-polyester mask, and a heavy cotton mask. Volunteers breathed into a sealed steel box, and the scientists then measured the humidity level inside it.
With no mask, the water vapor of exhaled breath filled the box, increasing humidity. But when the volunteers wore any of the 4 types of masks, humidity levels in the box declined because the masks trapped most of the water vapor in their exhaled breath. The researchers noted that the volunteers’ faces fit tightly against high-density foam rubber surrounding the opening in the box, eliminating leakage around the masks’ edges.
Increased humidity of inhaled air hydrates the respiratory epithelium, which is known to benefit the immune system. It also promotes the removal of mucus, and potentially harmful particles within it, from the lungs. High humidity can also enhance production of interferons that fight viruses.
“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,” coauthor Adriaan Bax, PhD, a biophysicist at the National Institute of Diabetes and Digestive and Kidney Diseases, said in a statement.