Wearing a well-fitting surgical mask underneath a cloth mask reduces potential exposure to Covid-containing respiratory droplets and aerosols by up to 96%, according to a new study from the Centers for Disease Control.
The CDC tested two different ways of wearing masks on dummies to see how they could make masks more effective: one was layering a cloth mask over a surgical mask (aka "double-masking"), and the other was knotting the ear loops of a surgical mask, then tucking in and flattening the material so it fits close to the face.
Both methods increased the effectiveness, and the researchers found that if two people are wearing tight-fitting surgical masks or double masking it can reduce exposure by about 96%.
To put this in perspective, N95 respirators that are used by healthcare workers and medical first responders fit very close to the face, forming a seal that filters 95% of airborne particles.
Surgical masks are made from a plastic-derived material called polypropylene. They're used to block splashes and keep germs from spreading in sterile medical environments. In experiments, a surgical mask blocked 42% of the particles from a simulated cough.
But the effectiveness of surgical masks can vary, "in part because air can leak around their edges, especially through the side gaps," according to the CDC. Adjusting the fit so that the surgical mask fit tightly around the face with no gaps reduced exposure by 82.2%.
There are other ways to make masks more effective, according to the CDC. Wearing a "mask fitter," which is a solid or elastic piece that fits over a surgical mask to create a tighter seal, can potentially increase the wearer's protection by 90%. Adding "a sleeve made of sheer nylon hosiery material" around your neck and over your nose and mouth on top of your surgical or cloth mask can also make the mask more effective.
Dr. Anthony Fauci, the nation's leading expert on infectious diseases, said that double-masking likely does provide enhanced protection, and called it "common sense," during an interview with NBC News' TODAY on Jan. 25.
These new findings are important as new more contagious variants of the virus emerge.