The U.S. Centers for Disease Control and Prevention recently changed their guidelines on whether healthy people should wear masks, suggesting that people cover their faces to help slow transmission of the novel coronavirus.The evolving view on face masks is just one more example of how quickly our understanding of the virus is changing. It also makes it hard for the public to know what information to take seriously. James Paton reports on what masks really do, why some still warn against their use, and how many people might be wearing them wrong.See omnystudio.com/listener for privacy information.