Back in the carefree year 2017, the USA Centers for Disease Control (CDC) produced the above guidance for healthcare workers who needed to wear masks for work, but favoured facial hear. It was motivated by Movember. The green ticks mean that the style of facial hair is compatible with wearing a fit-tested mask, the red crosses indicates that the style is not allowed, and those healthcare workers who need to mask-up at work will need to get the razor out. Most moustaches are allowed but almost all beards are banned as there is then facial hair where the mask has to fit tightly to the skin (see top left of image) to get a good seal and prevent air leaking around the edges.
This is for healthcare workers, and means many of them cannot have a beard. But beards are are allowed in the general public, and of course the public are now wearing masks, as well as healthcare workers (unlike in 2017). So, should bearded men, such as me, get the razor out? Prince and coworkers have studied this problem, to help us decide.
Figure 3 of Prince et al. is above. It shows the % of particles of a test aerosol* that are filtered out as a function of the length of beard of the man wearing it. FFE stands for Fitted Filtering Efficiency, i.e., filtering efficiency while worn. So the far-left-hand points gives how good a mask is when worn by a clean-shaven man, while on the far right, is the effectiveness for a man with a beard with hairs 10 mm or 1 cm long. This is a very nice piece of work by Prince and coworkers.
First of all, note that the filtering efficiency and fit of both cloth and procedure (also called surgical) masks are so bad, that growing a beard makes little difference. Unless your beard is Brian Blessed style** then the beard will make little difference. The mask filters so poorly and/or fits so badly that the beard does not matter.
The work of Prince and coworkers was done in the USA, and so they don’t consider the European standard of mask, the FFP2 and FFP3 standard***. But the FFP2 masks I wear are probably quite similar to the Korean standard KF94 and they did study a KF94 mask. There is a clear downward trend in how effective the mask is, with increasing bear length. And above beards of length of say 2 to 3 mm, there is a clear drop in effectiveness, with respect to how good they are if you are clean shaved.
I tend to set my beard trimmer to 3 mm, so if I am a bit less lazy and trim it more often, then my beard should reduce the effectiveness by no more than about 5%. The FFP2 mask should still reduce the amount of virus I inhale by about 80%, if I am sharing a room with someone infected with COVID-19. And given that the early signs are that the Omicron variant could be very infectious, I should do that. And you may also want to combine an FFP2 or KF94 or similar mask with not much than a very short beard.
* The test aerosol is a common aerosol of particles with a broad distribution of sizes but a median size around 50 nm. This is rather smaller than aerosols that we assume carry most virus but the FFE % should still be a good guide to how effective the mask is at filtering out virus containing particles.
** If so congratulations on the outstanding beard! But no mask will offer a lot of protection to the virus that causes COVID-19.
*** You may notice that the N95 – an American standard – offers the best protection. I think this may just because it fits better. I believe N95 masks are always/almost always worn with straps round the back of the head, not the eyes. This may help the mask fit better and so increase the % filtered, as even less leaks around the side than for a KF94, and results in much much less leakage than for a surgical/procedure mask.
Chance & Necessity 