If you have access to a mask, you should be wearing it whenever you go any place indoors except your house. There is a reason that Japan, who had its first cases the same time as the United States, has less than 2000 cases and fewer than 60 total deaths. Japan's population is about a third of the United States, but their infection and death rates are so low because EVERYONE wears masks when out. Same with Taiwan, South Korea, Singapore and Hong Kong. Use an N95 mask if you can get one, if not use any mask you can get. Viral loading matters and even a regular mask will prevent some loading.