Are cloth masks protective against SARS-CoV-2?


…but the full answer is a bit complicated.

There is a global shortage of protective personal equipment  (e.g. protective face masks, gowns, gloves) for clinicians handling patients. The recommended mask for handling COVID19 patients is a specialized mask known as an N95 respirator. Government failures to coordinate and stockpile these masks in event of a respiratory pandemic (the U.S., for example, stashed enough for 1% of the current need) have contributed to a significant shortage in supply. As production of N95 masks by manufacturers worldwide is at capacity, fashion companies and crafters are now trying to stem the protective gear shortage by making cloth masks.

Here is where it gets complicated. There is public and apparently corporate confusion about what these cloth masks are meant to achieve.The N95 mask is a tightly fitted nose and mouth mask made of multiple layers of electrostatically charged blown polymer fibers that catch 95% of all particles as small as 0.3 microns (um) (check out a history of the mask here). The SARS coronavirus is 0.125 nanometers or 0.000125 um in size. SARS-CoV-2 is typically carried in respiratory droplets (which are generally >5 um in size) and in lab settings, aerosols (<5 um). N95s catch these droplets over 0.3 um in size easily. The filtering ability of homemade cloth masks is very unclear, but it is extremely unlikely to reach 0.3 um. An examination of manufactured cloth masks found that particles smaller than 2.5 um were able to pass through the fabric. One study  found cloth masks failed to filter 97% of all particles 0.3-10 uM in size – meaning the cloth mask could not protect the wearer or people around them from virus alone transmitted by cough. The same study found cloth masks to be associated with higher risk of flu-like respiratory illness.

This shouldn’t be all that surprising. Surgical masks – of the earloop kind handed out in convenient care waiting rooms for patients with coughs – offer greater protection than cloth masks. The FDA has only approved surgical masks as protection for large water droplets and splashes. They too cannot filter out very small particles transmitted by cough.

However, via a cough, sneeze, “moist speaking“, or close breathing, virus in the respiratory tract is likely to be carried into the air in droplets or aerosols, not bare viral particles. There is increasing evidence that risk of this kind of transmission plummets with increased cloth or surgical masks use by the public. When everyone who can wears them and wears them without gaps and sags, cloth masks create multiple boundaries for droplets and aerosols to jump to enter a new respiratory tract.  This is true of the many grades of surgical masks as well.

The point of these fabric masks is not to replace N95 respirators or even surgical masks. The CDC has declared them a last resort respiratory protection for healthcare providers of COVID19 patients – that is, for last resort – marginally better than absolutely nothing – use. In this context, frequent exposure to high loads of virus is the risk for the wearer. This is a different level of risk than going to a grocery store. During the first days of blown polymer fabric shortages this past Spring, cloth masks were the only option for healthcare workers that would have otherwise worn surgical masks might have been used. As such mass manufacturers engaged in cloth mask production marketed  their masks as ntended for use in clinical settings when neither N95s or surgical masks are required.

Last resort is where practitioners many practitioners found themselves – and so some hospitals are collected, modified and stockpiled such handmade masks.

Bottom line –  If you are driven to sew masks for healthcare workers, check with the targeted facility first to see if they accept them and if they have a preferred pattern.

HH and JFB – March 26, 2020, long overdue update Sept, 2020.