People often argue that face masks are as effective against SARS-CoV-2 as a fence against mosquitoes because the viruses are much too small. It is not uncommon to read in the same text that masks do harm because they retain CO2 when you breathe it out.

What are the facts?

A SARS-CoV-2 virion has a diameter of 60 to 140 nanometres (nm). Converted into micrometres (μm), this is 0.06 to 0.14 μm.

An FFP3 mask filters out at least 99% of all particles larger than 0.6 μm This does not mean that everything smaller can get through without any problems, because one person can get through a door, but even two people can get through. So protective masks generally reduce the amount of virus particles that can pass through at the same time. The comparison with mosquitoes, on the other hand, is absolutely misleading, because mosquitoes are many times smaller than the meshes of a fence, than SARS-CoV-2 compared to the pores of a protective mask.

So what about carbon dioxide?

One CO2 molecule is 2 x 116.3 = about 232 picometres (pm) wide.

0.6 μm are 600,000 pm. So 2’586 CO2 molecules can pass through the pore of a mask at the same time without any problems.

Conclusion: the comparison with mosquitoes is misleading and those who are convinced that a mask retains a considerable amount of CO2 molecules should not worry about viruses. But let’s think about why surgeons can operate in a highly concentrated way at work without any oxygen deficiency symptoms.

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