Good question!
How does a facemask work?
Facemasks act as barriers between your airways and the environment and make it more difficult for viruses and bacteria to reach your airways.
Conversely, they also make it more difficult for them to leave your airways.
The fabric of a facemask acts as a filter, that removes larger liquid droplets from exhaled air and traps viruses that are present in those droplets.
However, viruses are extremely small (80-160 nanometers for coronaviruses), and the holes in the facemask filter are much bigger!
Still, facemasks can trap particles that are smaller than the gaps in the filter.
This is because they change the direction of airflow, so instead of infectious particles traveling in a straight line through the mask, they scatter in many different directions, causing many particles to ‘bump’ into the fabric of the mask. This principle applies especially to masks with multiple layers.
Finally, facemasks prevent you from touching your mouth and nose, and that can stop you accidentally infecting yourself that way.
How effective are facemasks?
How effective the facemask is depends on which type is being used.
Standard surgical masks stop approximately 80% of fine droplets.
FFP II (N95) and FFP III (N99) masks can stop 95 and 99% respectively.
These masks are typically only used in hospitals and laboratories, by personnel who have to come very close to sources of infection, under dangerous circumstances.
Wearing of facemasks by the public reduces the spread of the coronavirus, so the number of new cases per day. Studies have estimated that standard facemasks for the public are about 67% effective in protecting the wearer. This may not seem very high, but if everybody does it, we can slow the virus down together.
It is also important that masks are worn properly: so over the mouth AND the nose, make sure it fits tightly around your face, keep your mask in a clean place and make sure that the part of the mask you breath through doesn’t touch any potentially contaminated surfaces (including dirty hands).
