evidence: - The findings may help explain why wearing masks has been linked to lower disease severity in people with COVID-19. [...] Drs. Joseph Courtney and Adriaan Bax of NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) carried out a study to compare how different face masks affected the humidity of inhaled air. Results were published on February 12, 2021, in the Biophysical Journal. The scientists 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. A volunteer wore each mask for at least 10 minutes before any measurements were taken. The researchers then measured the level of humidity when breathing into a sealed steel box. The volunteer’s face was fitted tightly against the box using high-density foam rubber. Humidity measurements were taken at three different air temperatures, ranging from about 46 to 98 degrees Fahrenheit.