Hydrating the Respiratory Tract: An Alternative Explanation Why Masks Lower Severity of COVID-19 Disease

Abstract

Seasonality of respiratory diseases has been linked, among other factors, to low outdoor absolute humidity and low relative humidity in indoor environments, which increase evaporation of water in the mucosal layer lining the respiratory tract. We demonstrate that normal breathing results in an absorption-desorption cycle inside facemasks, where super-saturated air is absorbed by the mask fibers during expiration, followed by evaporation during inspiration of dry environmental air. For double-layered cotton masks, which have considerable heat capacity, the temperature of inspired air rises above room temperature, and the effective increase in relative humidity can exceed 100%. We propose that the recently reported, disease-attenuating effect of generic facemasks is dominated by the strong humidity increase of inspired air.SIGNIFICANCE STATEMENTFacemasks are the most widely used tool for mitigating the spread of the COVID-19 pandemic. Decreased disease severity by the wearer has also been linked to the use of cloth facemasks. This well-documented finding is surprising considering that such masks are poor at filtering the smallest aerosol particles, which can reach the lower respiratory tract and have been associated with severe disease. We show that facemasks strongly increase the effective humidity of inhaled air, thereby promoting hydration of the respiratory epithelium which is known to be beneficial to the immune system. Increased humidity of inspired air could be an alternate explanation for the now well-established link between mask wearing and lower disease severity.

Guidelines: Discharge Instructions for Covid-19 Patients

“…It is important to take prescribed medications and to maintain hydration as recommended. [134][135][136][137][138][139] Several weeks may be required before returning to a feeling of well-being consistent with that experienced prior to COVID-19. 2,132,[140][141][142] Selfisolation should continue to be practiced until resumption of regular daily activities is approved by a physician.…”

Higher Temperatures, Higher Solar Radiation, and Less Humidity Is Associated With Poor Clinical and Laboratory Outcomes in COVID-19 Patients

“…So, one can postulate that our finding of more severe COVID-19 with lower relative humidity and higher temperature is due to impaired mucosal defense that aids the virus in its infection and propagation. Effective humidity of inhaled air can modulate hydration of the respiratory epithelium that boosts mucosal immunity, so lower relative humidity and higher temperature can actually decrease mucosal hydration and impair it in return (28).…”