FFP2 masks offer an extremely high level of protection against corona infection.

But it depends on the correct way of wearing, as researchers from the Göttingen Max Planck Institute for Dynamics and Self-Organization report after a study.

If an infected and a healthy person meet in an indoor space at a short distance, the risk of infection is therefore a good one per mille (0.1 percent) even after 20 minutes.

The prerequisite is the correct fit of the FFP2 or KN95 mask, writes the team around institute director Eberhard Bodenschatz in the "Proceedings" of the US National Academy of Sciences ("PNAS").

With poorly fitting FFP2 masks, on the other hand, the risk of infection in the same scenario is around four percent, the team calculates. For optimal protection, the nasal clip must therefore be shaped into a "rounded W" so that it presses laterally on the nostrils. With surgical masks, a good fit is enough to reduce the risk of infection to a maximum of ten percent.

The researchers calculated the risk of infection by combining various factors such as particle sizes, physics when exhaling, various mask types and the risk of inhaling coronaviruses. "In daily life the actual probability of infection is certainly ten to a hundred times smaller," Bodenschatz is quoted in a communication from the institute. Because the air that flows out of the mask at the edges is diluted. However, the researchers wanted to calculate the risk as conservatively as possible. "If even the greatest theoretical risk is small under these conditions, you are on the safe side under real conditions," says Bodenschatz.

This is in contrast to the results of encounters between two people who are not wearing a mask: If, in this case, a healthy person stands three meters away in the breath of an infected person for a few minutes, there is a very high probability that they will be infected, according to the researchers.

Bodenschatz emphasizes: "Our results show once again that wearing a mask in schools and in general is a good idea."