Medical or surgical masks may help reduce the chance of spreading airborne diseases. Many wear them during flu season to avoid infecting others or being infected.
Disclaimer: On February 29, 2020, CDC published guidance strategies for optimizing the supply of N95 respirators to help prevent the spread of bacterial and viruses. This guidance provides Crisis Alternate Strategies that includes the option to "use of medical grade respirators approved under standards used in other countries that are similar to NIOSH-approved N95 respirators." Respirators, such as an N99, N95, PFF2(s), 3-Ply, KN95 and surgical masks, are designed to protect the wearer from inhaling or spreading airborne bacteria or virus particles.