Over the past year, mask-wearing has become essential for reducing the transmission of the virus responsible for COVID-19. Authors Joseph M. Courtney and Ad Bax from the National Institutes of Health (NIH) have recently proposed a novel, physical mechanism to explain the largely reported decrease in the severity of COVID-19 for those who wear masks. The authors claimed that the microenvironment created by wearing a mask has a higher relative humidity, promoting action of the immune system and clearance of the mucous membrane (Courtney and Bax).
From childhood, we have become accustomed to the fact that during the colder months we can anticipate more sniffling and coughing than any other time of the year. Interestingly, this seasonal uptick in sickness can be attributed, at least in part, to the decrease in ambient humidity. Humidity refers to the water content in the air, and warmer air has a higher capacity for holding water. Thus, when the air is cold—as in the wintry months—the lack of moisture in the air essentially draws water from the cells in your body, generating the perfect conditions to permit the spread of virus-containing particles to the lungs. This can cause severe infection.
It is widely known that wearing a face covering mitigates severe COVID-19, and the authors suggest that this is due to an increase in the humidity of inspired air—the air taken in during inhalation. To test this hypothesis, Courtney and Bax had subjects breathe into a specially-constructed chamber while wearing either no mask or one of four different types of masks. During this process, the authors took measurements of the humidity in the chamber and observed how humidity increased over the course of regular breathing (Courtney and Bax).
Their measurements showed that the humidity increase in the chamber is substantially lessened for masked breathing versus unmasked breathing. This result indicates that the water from the subjects’ exhaled air must be trapped within the mask, rather than escaping into the chamber (Courtney and Bax).
In order for this stored water to rehumidify the low-humidity ambient air being breathed in to the extent reported in the paper, a mask must also have a sufficient capacity for storing heat—as previously mentioned, warmer air holds more water. Unsurprisingly, the authors reported that the temperature of the mask—measured quickly after removing it from the subject subsequent to breathing—yielded temperatures more than triple that of the room temperature (Courtney and Bax).
Taken altogether, these results support the notion that wearing a mask does increase the humidity of inspired air, preventing mucosal membrane cells from drying out and engendering the ideal circumstances to mount an immune response and deal with a viral infection.
While it is broadly accepted that masks decrease the severity of COVID-19, the explanation of decreased viral load leading to a diminished disease state is incomplete and does not account for the permeability of non-medical-grade face coverings. Courtney and Bax, however, offer an alternative, more plausible mechanism for why face masks can be effective in this regard. Their findings have potentially reaching implications for preventing severe infection in other seasonal respiratory viruses.
Works Cited
Courtney, J.M., Bax, A. “Hydrating the respiratory tract: An alternative explanation why masks lower severity of COVID-19.” Biophysical Journal, vol. 120, no. 6, 2021, https://doi.org/10.1016/j.bpj.2021.02.002.
Last Fact Checked on May 22nd, 2021.