Why wearing a face mask lowers Covid-19 disease severity

We wear masks in the pandemic primarily to protect those around us. COVID-19 spreads mainly from person to person through respiratory droplets. Respiratory droplets travel into the air when you cough, sneeze, talk, shout, or sing. These droplets can then land in the mouths or noses of people who are near you or they may breathe these droplets in.

Masks are a simple barrier to help prevent your respiratory droplets from reaching others. Studies show that masks reduce the spray of droplets when worn over the nose and mouth.

It is especially important as we know that many with an acute Covid-19 infection are asymptomatic (never develop symptoms) or presymptomatic ( haven’t developed symptoms yet) but can still transmit the virus to others.

It has also been considered that wearing a mask may also protect us too but there, as yet, has not been any evidence to prove this. Most of us would consider it slightly protective as it stops those droplets reaching two areas where the virus particles get into our bodies - the nose and mouth.

In a recent paper published in Biophysical Journal “Hydrating the respiratory tract: an alternative explanation why masks lower severity of COVID-19” Bax et al put forward some evidence.

The researchers show that using face masks strongly increases the effective humidity of inhaled air, providing an explanation of why wearing masks has been linked to lower disease severity in people infected with SARS-CoV-2.

The study evaluated four types of masks: an N95 mask, a surgical mask, a light cloth mask and a heavy cotton mask. The level of humidity was measured by having a volunteer breathe into a sealed box. When the person wore no mask, the water vapour of the exhaled breath filled the box, leading to a rapid increase in humidity inside the box.

The results showed that all masks increased the level of humidity of inhaled air, but to varying degrees. At all temperatures, the heavy cotton mask led to the most increased level of humidity in the inhaled air.

The researchers report a strong correlation between increased COVID-19 severity and low humidity of inhaled air, although much debate remains about the relative importance of the various season-related factors on its transmissibility and severity.

They propose that the increased humidity of air inspired through face masks is responsible for the lower disease severity of mask wearers.

So until we are all vaccinated against SARS-CoV-2 it is now especially prudent, with the relaxing of lockdown measures, that we continue to wear masks, wash our hands frequently and observing social distancing.


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