Reference:

Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med 26, 676–680 (2020). https://doi.org/10.1038/s41591-020-0843-2

Experimental Design:

Researchers randomly assigned 246 volunteers to two groups. Some had already been infected with seasonal coronavirus (NOT the kind that results in COVID-19), the flu, or the common cold. In the first group, people were asked to breathe normally without a mask. Researchers then collected their breath samples and tested them for coronaviruses and influenza. The second group was told to do the same, but while wearing surgical masks.

Results:

Wearing a mask made a huge difference!

• When infected people breathed, viruses were found in 26-30% of their saliva droplets and 40-56% of their aerosols.
• The no-mask group had 10 people infected with seasonal coronavirus. Traces of the virus were found in 30-40% of their breath samples.

• The masked group had 11 people infected with seasonal coronavirus. Because they wore a mask, no virus was found in their breath samples.

What does this mean?

Wearing a surgical or cloth mask in public does not guarantee that you won’t catch COVID-19. But it’s still the best way to protect yourself and others.

In the next section, learn more about how to best wear a mask to maximize protection.

Up Next: Why is mask fit important?

back to mask guides

next section