• Face masks reduce the expulsion of respiratory aerosols (called source control).
• Poorly fitted masks allow respiratory aerosols to escape through face seal leaks.
• Fit modifications improve the performance of face masks as source control devices.
• Unmodified medical masks blocked ≥56% of cough aerosols and ≥42% of exhaled aerosols.
• An elastic brace over a mask blocked ≥95% of cough and ≥99% of exhaled aerosols.”