Guidance on the use of face masks has evolved along with the Covid-19 pandemic. Initially, most authorities advised that masks be used only if you were a healthcare practitioner in close contact with patients, if you were coughing or sneezing, or if you were taking care of a person with a suspected Covid-19 infection. More recently, we have been advised to use masks in situations where it is not possible to maintain the prescribed two-metre physical distance. All in all, the demand for masks has increased, including demand for particulate respirators such as the ones pictured. These masks became controversial when 3M pushed back against a request from the US administration to halt exports, saying the move would cut off critical supplies for neighbouring countries and raise “significant” humanitarian concerns. Photograph: Justin Chin for Bloomberg