Wearing two face masks at the same time can help prevent the spread of COVID-19, both for people who are wearing masks and for people who are not. Whether or not this approach is effective depends on the type of mask you wear.

Two experiments done by the United States Centers for Disease Control and Prevention (U.S. CDC) released in February of 2021 found that wearing a cloth mask over a disposable surgical mask offered significant rates of protection. As part of this experiment researchers put together two head-shaped devices called "headforms" in close confinement. One of the devices simulated a coughe. When headform #1 was maskless and headform #2 wore a cloth mask over a surgical mask, that mask blocked 85.4% of cough particles.

When both headforms wore a cloth mask over surgical mask, the headform getting coughed on had a 95% lower exposure than they would have if neither person wore a mask.

In the study, wearing a cloth or surgical mask alone blocked 51.4% and 56.1% of particles from the cough. This suggests wearing the two types of masks on top of each other can dramatically increase the amount of protection for the mask wearer and the people around them.

Importantly, wearing two surgical masks is not recommended. Wearing two snug cloth masks over each other should help improve protection for the mask wearer and the people around them.

It should be noted that wearing any type of mask is much more effective than going maskless. The U.S. CDC recommends focusing on improving how masks fit to further reduce exposure to viral particles. Masks should fit well and hug your face without causing any gaps that could allow the virus to escape or enter. The less air that leaks through the face seal, the better.

Masks work by blocking COVID-19 from spreading through mouths and noses of infected people. The virus spreads through very small amounts of liquid called respiratory droplets and they usually fall onto the ground and surfaces around them after a person coughs, talks, sings, or even breathers.

Doing the above activities also produces even smaller droplets called aerosolized particles that are lighter and drier than respiratory droplets, so they tend to stay in the air for several hours.

These different droplet sizes can land on others, stay in the nearby air, or land on surfaces a person might touch before they touch their face (especially their nose and mouth). Masks serve as a type of barrier to the droplets. They increase the amount of filtration between a person's mouth and nose and the outside air, so fewer particles—like the virus that causes COVID-19—can pass through. Adding more layers of material through wearing a second mask can increase the amount of protection people have through blocking exposed particles and inhalation of these particles.