To stop infected people (some don’t even know) from expelling virus. Even if not sneezing or coughing simply talking sends droplets out.
To help remind you not to touch your face – the SARS-COVID-19 virus can enter your body through nose and mouth (yes and thru eyes). Once in ….
If you are going to get infected better to get it in a small dose – ‘start small’ a low inoculum. This gets your immune system going to stop the intruder-the virus. A small inoculum allows your body to mount a defense and start making antibodies to the virus.