In laboratory simulations, face shields blocked only 2% of exhaled cough aerosols, whereas N95 respirators blocked 99% and medical masks blocked 59%. Comparison: Face Shields vs. Masks
The Centers for Disease Control and Prevention (CDC) and other health authorities do not recommend face shields as a primary substitute for cloth face coverings because they lack a peripheral seal.
Simulations show that high-velocity vortex rings produced by a sneeze can reach the top and bottom edges of a shield in just one second. If a wearer inhales as these particles arrive, they can draw infectious air directly behind the shield.
Studies published in journals like Physics of Fluids highlight several critical reasons why face shields fail as standalone protection:
Research on the efficacy of face shields confirms that while they are excellent for blocking large splashes, they are in preventing the spread of airborne pathogens like COVID-19.
While shields block the initial forward "jet" of a cough or sneeze, smaller aerosolized droplets can easily flow around the sides and bottom of the visor.