Scott Alexander reviews evidence on face mask effectiveness against coronavirus, concluding they likely offer some protection despite CDC recommendations against general public use. Longer summary

This post examines the effectiveness of face masks in preventing coronavirus transmission. It reviews theoretical reasons, case-control studies, randomized trials, and laboratory studies on surgical masks and N95 respirators. The author concludes that while not perfect, surgical masks likely offer some protection against infection in high-risk situations. The post also discusses the CDC's recommendations against mask use for the general public, suggesting this may be due to high standards of proof in medical communication rather than intentional deception. The author ultimately recommends considering mask use in high-risk situations if supplies are not limited, while emphasizing that masks are not a substitute for avoiding such situations when possible. Shorter summary