We know that when we wear a face mask, we protect ourselves and others from the virus that causes COVID-19. A new study supported by the National Institutes of Health (NIH) suggests that one way masks may protect us is by increasing the humidity of the air we inhale. The higher level of humidity, which comes from our breath, may increase our protection against diseases such as COVID-19.

The study researchers cited prior research that found that higher humidity can help the lungs clear out germs and mucus, which helps delay and reduce infection.

At all temperatures, the heavy cotton masks led to the most increased level of humidity.

“The increased level of humidity is something most mask-wearers probably felt without being able to recognize it, and without realizing this humidity might actually be good for them,” said the study’s lead author, Adriaan Bax, Ph.D., NIH Distinguished Investigator.

Dr. Bax and his team tested four common types of masks. They tested N95 masks, three-ply disposable surgical masks, two-ply cotton-polyester masks, and heavy cotton masks. All four types increased the level of humidity of inhaled air, but to different levels. At lower temperatures, the humidifying effects of all the masks greatly increased. At all temperatures, the heavy cotton masks led to the most increased level of humidity.

“This research supports the importance of mask-wearing as a simple yet effective way to protect the people around us and ourselves from respiratory infection,” said Griffin P. Rodgers, M.D., director of NIH’s National Institute of Diabetes and Digestive and Kidney Diseases.