To mask or not to mask - Part 2

Earlier I wrote that using masks to prevent spread of infections makes a lot of sense.  But it turns out, prolonged use of masks may actually increase the risk of infection from respiratory virus.  Dr. David Fein of Princeton Longevity Center, has nicely summarized a couple of papers published on use of face masks. 

In one study, which looked at the impact of using face covering on three types of viruses - seasonal Corona virus, Rhinovirus and Influenza virus, the researchers concluded that

...seasonal coronaviruses can be transmitted in aerosols produced during normal breathing. However, even without a face mask, there were low amounts of viral shedding from people with influenza virus and seasonal coronavirus in both aerosols and respiratory droplets...

But another study served up some disconcerting information. In observing the effect of cloth masks and medical-grade masks in healthcare workers, the researchers found that

...that cloth masks increase the risk of infection from influenza-like-illnesses. The increase is thought to stem from a 97% rate of particle penetration with cloth masks as well as increased moisture retention observed and the frequency and effectiveness of cleaning between uses...

So, while it may be advisable to use face covering when in crowded areas, it seems it may not be good to keep it on for a long time due to the increased risk of particle penetration and increased moisture retention.  As for effectiveness of cleaning, it is better to clean the mask in washing machine in hot cycle, as recommended by the CDC, rather than hand wash them.