Masks help the people who wear them to spread SARS-CoV-2, the virus that gets COVID-19, but now researchers from the National Institutes of Health have added evidence for another potential benefit to carriers: the humidity contained in the mask can help fight respiratory diseases such as COVID-19.
The study, led by researchers from the NIH’s National Institute for Diabetes and Digestive and Kidney Diseases (NIDDK), found that face masks significantly increase the humidity in the air in which the mask wearer breathes. This higher humidity level in inhaled air, the researchers suggest, may help explain why wearing masks has been linked to lower severity of disease in people infected with SARS-CoV-2, as airway hydration is known to immune system benefits. The study published in the Biophysical Journal.
“We found that face masks greatly increase the humidity in inhaled air and suggest that the consequent hydration of the respiratory tract may be responsible for the documented finding linking the lower severity of COVID-19 disease to wearing a mask,” said the principal’s author Adriaan Bax, Ph.D., NIH Distinguished Investigator. “High levels of humidity have been shown to alleviate the severity of the flu, and this may apply to the severity of COVID-19 through a similar mechanism.”
Can high humidity limit the spread of a virus to the lungs by promoting mucosal clearance (MCC), a defense mechanism that removes mucus? and possibly harmful particles within the mucus? from the lungs. High humidity levels can also boost the immune system by producing special proteins, called interferons, that fight viruses? a process known as the interferon response. Low humidity levels have been shown to impair both the MCC and the interferon response, which is one of the reasons why people in cold weather are prone to contract respiratory infections.
The study tested four common types of masks: an N95 mask, a three-layer disposable surgical mask, a two-layer cotton-polyester mask, and a heavy-duty cotton mask. The researchers measured the humidity level by having a volunteer breathe in a sealed steel box. When the person was not wearing a mask, the water vapor from the exhalation filled the box, leading to a rapid increase in humidity in the box.
When the person wore a mask, the buildup of moisture in the box decreased significantly because most of the water vapor remained in the mask, condensed and inhaled again. To ensure no leakage, the masks with high density foam rubber were applied to the face of the volunteer. Measurements were made at three different air temperatures, ranging from about 46 to 98 degrees Fahrenheit.
The results showed that all four masks increased the humidity of inhaled air, but to varying degrees. At lower temperatures, the moisturizing effects of all masks increased sharply. The thick cotton mask led to the highest level of humidity at all temperatures.
“The increased humidity level is something that most mask wearers probably feel without being able to recognize, and without realizing that this humidity may actually be good for them,” Bax said.
The researchers did not look at which masks are most effective against inhalation or transmission of the virus, and referred to the CDC for guidance on choosing a mask. Earlier studies by Bax and his colleagues showed that any cloth mask can help block the thousands of saliva drops that humans release through simple speech? droplets which, if released, can remain in the air for many minutes. While the current study did not examine respiratory drops, it does provide more evidence as to why masks are essential to combat COVID-19.
“Even as more people are vaccinated nationwide, we need to be vigilant to do our part to prevent the spread of the coronavirus that causes COVID-19,” said Dr. Griffin P. Rodgers, director of the NIDDK, said. “This research supports the importance of wearing a mask as a simple yet effective way to protect people around us and to protect ourselves from respiratory infection, especially during these winter months when susceptibility to these viruses increases.”
The research was supported by the NIDDK Intramural Research Program and the NIH Intramural Antiviral Target Program.