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In the fight against coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), one of the weapons used by humans to prevent infection is wearing a face mask. Although many countries do not require this infection control measure, it can help protect against inhalation of virus-laden droplets and aerosols.
A new study, published in the journal Biophysical Journal by researchers from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health (NIH), showed that face masks increase the humidity in the air that wearers of mask inhale. The level of humidity in inhaled air could be linked to lower levels of COVID-19 severity.
Humidity and respiratory diseases
The seasonality of respiratory diseases is linked to low outdoor absolute humidity and low indoor relative humidity. During these periods, there is an increase in the evaporation of water in the lining of the respiratory tract.
Hydration of the airways is known to benefit the immune system. High levels of humidity can reduce the spread of a virus to the lungs. It promotes mucociliary clearance (MCC), a body defense mechanism that removes mucus and particles from the lungs.
Apart from this, high humidity can stimulate the immune system to produce special proteins called interferons. These fight viruses in a mechanism called the interferon response and may explain why it is more common for people to get respiratory infections in the winter or cold season.
Moisture in face masks
Researchers have shown that the fibers in the mask absorb normal breathing, resulting in an absorption-desorption cycle inside face masks, in which supersaturated air during exhalation and evaporation during inhalation. dry ambient air.
The researchers tested four types of masks common in the study, including the N95 mask, a three-layer surgical mask, a two-layer cotton-polyester mask, and a heavy cotton mask. They asked volunteers to breathe out into a sealed steel box to measure the humidity level.
The team took measurements at three temperatures between 46 ° F and 98 ° F. They found that when the volunteers wore a mask, the moisture build-up in the box decreased markedly. In addition, all four masks tested increased the humidity level of the inhaled air to varying degrees.
For double-layered cotton masks, which have a considerable heat capacity, the temperature of the inhaled air exceeds the ambient temperature. The actual increase in relative humidity can exceed 100%.
“We propose that the recently reported disease alleviation effect of generic masks is dominated by the large increase in the humidity of inspired air. This high humidity promotes mucociliary clearance of pathogens from the lungs, both before and after an upper respiratory infection, ”the researchers wrote in the article.
When mucociliary clearance is successful, it can delay and reduce infection of the lower respiratory tract, limiting the severity of the disease. Masks can serve as protection against respiratory droplets and, at the same time, reduce the risk of infection by increasing humidity levels.
“We found that face masks greatly increase the humidity of inhaled air and suggest that the resulting airway hydration may be responsible for the documented finding that links the lower severity of COVID-19 disease to wearing of a mask, “Dr. Adriaan Bax, Distinguished NIH Investigator, said.
“High humidity levels have been shown to mitigate the severity of influenza, and this may apply to the severity of COVID-19 through a similar mechanism,” he added.
Also, the increased humidity level is something that most people wearing masks experience without realizing that it can reduce the risk of infection.
“This mode of action suggests that masks may benefit the wearer even after an upper respiratory infection has occurred, complementing the traditional function of masks to limit person-to-person transmission of disease. This potential therapeutic use should be investigated further, ”concluded the researchers in the study.
Wearing face masks is part of the global campaign to adhere to infection control measures. While vaccines are in the process of being rolled out, prevention of infection may rely on protecting oneself against carriers of SARS-CoV-2. In addition to wearing masks, regular hand hygiene and physical distancing can reduce the risk of infection.
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