< Masks

What kind of mask should we put on in what situation?

Text updated on 2021-02-07

There are three categories of masks:

See the question What are the different types of masks?

In deciding which mask to use in which situation, the most important thing to consider is the ability of a mask to prevent the spread of the virus, i.e., its filtering power and adherence to the face, and the level of risk of the situation you are in. Particles should not be able to enter or exit through or around the mask. Adhesion to the face is an important factor: if there is just a small gap between the mask and the face, about a centimeter in size, this can reduce the effectiveness of the mask by 60%. Therefore, care must be taken not to cross the elastics of surgical masks to shorten them. The mask may "yawn" at the sides and no longer fit the face. To shorten the elastics, it is better to tie a knot on the elastic itself. The masks with the greatest filtering capacity are respirators, but they are also the least comfortable for prolonged use. Fabric masks are generally less filtering than surgical or FFP2 masks. With the emergence of new coronavirus variants (see the question What are the SARS-CoV-2 coronavirus variants that have attracted attention? and the question What do we know about the UK variant?), it is likely that coronavirus transmission will become increasingly easier between people, so it is wise to protect yourself and others with effective masks!

The risk depends on the number of people around us (the higher the density, the higher the risk), the sound volume (the louder the volume, the higher the risk), the size of the room (the smaller the room, the higher the risk), the ventilation of the place (the less ventilation, the higher the risk), the time spent (the longer the time, the higher the risk), and our activity (the more out of breath, the higher the risk). See the question How do we assess risks in our daily lives?

Depending on the risk level of everyday situations (high, moderate, low), different types of masks can be worn: high-risk situations with an FFP2 mask, moderate-risk situations with a surgical mask and low-risk situations with a fabric mask.

The following is a decision aid for deciding which type of mask to use in the following situations:

To be effective, the mask must cover the nose and mouth well. If you need to make a phone call, do not remove your mask. Sound passes well through the mask.

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A man who had put his mask on incorrectly was contaminated during a flight from Singapore to Hangzhou, China on January 24, 2020. On the plane, he sat with his mask in the wrong position for an hour next to two asymptomatic people who then tested positive for SARS-CoV-2 coronavirus, because he talked to his wife and child who were next to him. The other people sitting next to the infected people were not infected. They all wore masks.

Chen, J., He, H., Cheng, W., Liu, Y., Sun, Z., Chai, C., ... & Shi, X. (2020). Potential transmission of SARS-CoV-2 on a flight from Singapore to Hanghzou, China: An epidemiological investigation. Travel Medicine and Infectious Disease, 101816.

Study of 961 patients with COVID-19 in Hong Kong between December 2019 and April 2020 and the cause of their contamination. Non-masked" leisure activities, such as eating and drinking in restaurants and bars, singing in a karaoke bar, or playing sports in a gym, led to significantly more cases of contamination than "masked" work environments.

Cheng, V. C., Wong, S. C., Chuang, V. W., So, S. Y., Chen, J. H., Sridhar, S., ... & Yuen, K. Y. (2020). The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2. Journal of Infection.

Study of two groups participating in an event, each group being in a different bus for 1h30 with a single asymptomatic case COVID in one of the buses. The probability of being infected was multiplied by 11.4 in the bus with the infected person, regardless of the distance to the infected person, demonstrating aerosol contamination in an enclosed space for an extended period of time.

Shen Y, Li C, Dong H, et al (2020) Community Outbreak.

Filtration measurements of different types of masks according to the presence or absence of fit leaks. Leaks reduce the filtration power by about 50%.

Konda, A., Prakash, A., Moss, G. A., Schmoldt, M., Grant, G. D., & Guha, S. (2020). Aerosol filtration efficiency of common fabrics used in respiratory cloth masks. ACS nano, 14(5), 6339-6347.

Video that explains how to shorten a surgical mask to make it fit better to the face and therefore more protective. The method can also be used to transform an "adult" size mask into a "child" size mask. The video is in English but the image is enough to understand.


Classification of situations according to the risk of contamination.

Jones, N. R., Qureshi, Z. U., Temple, R. J., Larwood, J. P., Greenhalgh, T., & Bourouiba, L. (2020). Two meters or one: what is the evidence for physical distancing in covid-19?. bmj, 370.