The evidence suggests that broad mask mandates have not done much to reduce Covid caseloads over the past two years. Today, mask rules may do even less than in the past, given the contagiousness of current versions of the virus. From the beginning of the pandemic, there has been a paradox involving masks. As Dr. Shira Doron, an epidemiologist at Tufts Medical Center, puts it, "It is simultaneously true that masks work and mask mandates do not work." To start with the first half of the paradox: Masks reduce the spread of the Covid virus by preventing virus particles from traveling from one person's nose or mouth into the air and infecting another person. You would think that communities where mask-wearing has been more common would have had many fewer Covid infections. But that hasn't been the case. In U.S. cities where mask use has been more common, Covid has spread at a similar rate as in mask-resistant cities. Mask mandates in schools also seem to have done little to reduce the spread. Hong Kong, despite almost universal mask-wearing, recently endured one of the world's worst Covid outbreaks. Because masks work and mandates often don't, people can make their own decisions. Anybody who wants to wear a snug, high-quality mask can do so and will be less likely to contract Covid. That approach one-way masking " is consistent with what hospitals have long done. Patients, including those sick with infectious diseases, typically have not worn masks, but doctors and nurses have.