A viral video shows a UK doctor discuss the relative benefits of different face coverings with two colleagues, one of whom is claimed to be a “trainer and fit tester for qualified masks.”
During the video they look at three masks. One is a surgical mask, typically a loose fitting blue mask the likes of which are commonly available.
The second is a surgical mask with an attached sheet of plastic which acts as a visor to protect the eyes.
The third is an FFP3 disposable respirator, which looks like a mask but forms a seal with the face, stopping particles from getting in through the sides.
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What is claimed about the masks?
The people in the video claim that surgical masks don’t offer any protection for the wearer against the new coronavirus, whereas FFP3 respirators do.
A surgical mask, in theory, will help block large droplets and keep them from reaching your mouth and nose. However it will not filter or block small particles in the air which could contain the Covid-19 virus.
How that theory applies to the real world is more complicated.
A study in the Lancet found that masks have been shown to protect the wearer against infection, looking primarily at studies in healthcare settings. They are less effective than respirators, and by no means 100% effective at reducing infection, but there is evidence to show they help.
The evidence on how useful masks are outside of healthcare settings is less consistent but there is some evidence of benefit. For example, a review of studies into mask wearing to control influenza transmission found “no significant effect”. Another (which has not yet been peer-reviewed) found some evidence that there might be a slight protective effect against respiratory infections and a third review of existing studies in both healthcare settings and the community again found “no significant effect” (it has also not yet been peer reviewed).
These studies typically look at whether masks stop infection outright, which might not tell the whole story. Research suggests that masks could be effective even if they just reduce the number of viral particles that make their way into the wearer’s body, which may result in the wearer having a milder infection or not getting infected at all.
The evidence on FFP3 respirators is much clearer. FFP3 respirators remove at least 99% of particles when inhaling, and so offer the most protection against Covid-19 infection.
While surgical masks are used as personal protective equipment in hospitals, FFP3 respirators are recommended for staff who are dealing with Covid-19 patients and “for all aerosol generating procedures” due to this level of protection.
Masks may offer the most benefit by protecting others
What is clear about the video is that the staff are only considering the value of masks to the wearer. A mask which is deemed not to adequately protect the wearer is dismissed as “no good”.
They say that people don’t really need to wear surgical masks in public, as is being recommended by various governments including the UK government.
This is arguably unhelpful, because it ignores the evidence showing that wearing a mask can also help other people, not just yourself.
One theory as to why masks might be better at protecting others rather than yourself relates to the transmission of Covid-19.
When you breathe, cough, sneeze or talk you expel droplets which can evaporate and become smaller “droplet nuclei”.
Transmission of disease via droplets is known as droplet transmission, and via smaller droplet nuclei is also known as airborne transmission. There is mounting evidence that Covid-19 is spread by airborne transmission as well as droplet transmission.
Masks are better at stopping droplets than droplet nuclei, because droplets are bigger.
So a mask may not protect you from breathing in an airborne infected droplet nucleus. But, if you yourself are infected, a mask might stop the droplets you sneeze out, before they can turn into droplet nuclei which could infect someone else.