Wearing face coverings outside should be normalised because it may reduce transmission of SARS-CoV-2 in some situations and may encourage mask wearing indoors, where risks are greater say Babak Javid, Dirk Bassler, and Manuel B Bryant. But Muge Cevik, Zeynep Tufekci, and Stefan Baral argue that outdoor transmission contributes very little to overall infection rates and that efforts should focus on reducing indoor transmission