According to the World Health Organization, respiratory infections, such as Covid-19, can be transmitted through droplets emitted by an individual during a conversation, a sneeze or a coughing fit.
Augustin Charvet, University of Lorraine; Dominique Thomas, University of Lorraine and Nathalie Bardin Monnier, University of Lorraine
These droplets emitted by respiratory activities have a wide size range from a few tens of nanometers to a few hundreds of micrometers. The finest of these droplets can remain suspended in the atmosphere for several hours and thus travel significant distances depending on the conditions (anemometry, temperature, humidity).
Recent studies have also demonstrated the viability of the SARS-CoV-2 virus in these droplets over several hours. Therefore, wearing a mask is recommended to avoid the emission as well as the reception of these contaminated droplets emitted by an infected person and thus limit the spread of the virus.