Wearing masks can help reduce the transmission of COVID-19 as well as protect the wearer from disease. New research from the National Institutes of Health found that the humidity generated from wearing a face mask can also potentially reduce the severity of the disease if you do get sick.

The study, lead by researchers at NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), discovered that face masks significantly increase the levels of humidity that the wearer breathes in. This may explain why people who wear masks appear to suffer less severe cases of COVID-19.

According to the National lnstitutes of Health, keeping the respiratory system hydrated boosts the immune system. Researchers published their findings in the Biophysical Journal, and said that the elevated humidity of the air the face mask wearer breathes in helps clear away pathogens and “reduces infection in the lower respiratory tract, thus mitigating disease severity.”

The authors also noted that wearing cloth masks, which do not filter aerosol particles as well as surgical masks, is also associated with a reduced risk of severe disease. They said that high levels of humidity have been linked to diminished severity of the flu, and it’s likely that the same  mechanism that is applicable to COVID-19.

The researchers tested four masks including an N95 respirator, a disposable surgical mask, a two-ply cotton and polyester mask, and a cloth mask. While all four masks raised the levels of humidity the wearer inhaled, they were most elevated with the cloth mask.

“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 susceptibly to these viruses increases,” said NIDDK director, Dr.  Griffin P. Rodgers.

Australian researchers conducted an earlier study on how humidity affects the transmission of SARS-CoV-2, the virus that causes COVID-19. The scientists found that for every 1% decrease in relative humidity, COVID-19 cases could jump by 7 or 8%.

Professor Michael Ward, of the University of Sydney, said we could face increased risks of coronavirus community transmission when humidity is low or when the air is dryer, according to a news release from the university.

“Dry air appears to favor the spread of COVID-19, meaning time and place become important,” said Ward. “Accumulating evidence shows that climate is a factor in COVID-19 spread, raising the prospect of seasonal disease outbreaks.”

Professor Ward explained that drier air makes aerosol particles that are emitted when you cough or sneeze smaller and lighter so they can travel greater distances and stay suspended in the air longer.

The Centers of Disease Control and Prevention also published research that showed the coronavirus was more stable in low-temperature and low-humidity situations, whereas warm temperatures and higher humidity shortened the lifespan of SARS-CoV-2.