This is to keep your micro droplets away from other people: "In response to new guidance from the California Department of Public Health, the Marin County Department of Health and Human Services (HHS) and Bay Area health officials are recommending that residents cover their nose and mouth when leaving home for essential travel, such as doctor appointments, grocery shopping or pharmacy visits. Resident face coverings do not have to be hospital grade but need to cover the nose and mouth. Home-sewn fabric coverings, bandanas, a “DIY” mask from an old t-shirt and neck gaiters are examples of acceptable face coverings, especially because they can be washed and worn again."
FULL UPDATE: https://coronavirus.marinhhs.org/sites/default/files/2020-04/covid-19-status-update-4-3-2020.pdf
MICRO DROPLET MOVEMENT:https://www.youtube.com/watch?v=vBvFkQizTT4&feature=emb_logo