According to the CDC, it is recommended to wear face mask in public settings where other social distancing measures are difficult to maintain, like at grocery stores and pharmacies.
Physical distancing (maintaining at least 6-feet away from others) is still required, even when wearing a mask.
Supplies of hospital-grade masks for health care workers must continue to be a priority, but extra surgical masks or homemade masks of multilayered cotton will likely provide more protection compared to wearing nothing during this epidemic. It is important to avoid wearing a mask that contains a valve (typically a raised plastic cylinder about the size of a quarter on the front or side of the mask) that is designed to facilitate easy exhaling. The latest Order of the Public Health Officer in San Francisco (C19-12 "Requiring Face Covering") specifically prohibits masks of this type. Valves permit droplet release from the mask, putting others nearby at risk.