Skip to main content CDC's mask guidance may come as a 'psychological shock.' But here's the data behind it FacebookTwitterEmail 1of2 Pedestrians wear face coverings on Mission Street in San Francisco in February.Scott Strazzante/The ChronicleShow MoreShow Less 2of2 People wear masks as they stroll around Lake Merritt in Oakland in January. California has not yet changed mask rules following the CDC’s announcement.Gabrielle Lurie/The ChronicleShow MoreShow Less When historians reflect back on these chaotic COVID times, May 13 may stand out as particularly memorable: the day federal health officials said most Americans can ditch their masks, the clearest signal after more than a year of restrictions that the end of the pandemic was at hand.