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Public health measures to curb the spread of coronavirus have emphasized that masks are essential. By reducing both the spread and inhalation of infectious droplets, mask wearers are less likely to engage in contagious interactions.
Recently, White House advisor Dr. Anthony Fauci recommended that if one mask is effective, two could be even better. “If you have a physical covering with one layer, adding another layer simply makes sense, as it’s likely to be more effective,” Fauci shared with Today. “That’s why many people are either double masking or opting for an N95 version.”
Fauci's remarks came after several prominent figures, including attendees at President Joe Biden's January 20 inauguration, were seen wearing two layers of masks, typically a surgical mask paired with a cloth mask. In February, the Centers for Disease Control recommended double-masking to further prevent the spread of the virus.
Dr. Monica Gandhi, an infectious disease expert and professor at the University of California, San Francisco, believes the advice is solid—if done correctly.
“The goal is to enhance both the mask's fit and filtration by combining a surgical mask with a cotton one,” Gandhi explains to Mytour. “The surgical mask, made of polypropylene, repels the virus electrostatically, while the cotton mask fibers physically block it. The fit improves by securing both masks with two layers.”
The term 'double-masking' is somewhat misleading. While technically correct, the purpose is to add a filtering layer over a cloth mask. Surgical masks, commonly used in healthcare settings, offer filtering similar to N95 masks, though they are in short supply. However, surgical masks do not fit the face very well. Adding a homemade cotton mask on top allows the wearer to benefit from the polypropylene layer while reducing gaps around the nose and cheeks.
Cloth masks worn with a surgical mask or another polypropylene filter offer enhanced protection. | Courtesy of Monica Gandhi.The effect is similar to cotton masks that already include a polypropylene layer. If you’re using one of these homemade masks, double-masking is unnecessary, according to Gandhi.
In a recent commentary [PDF] co-authored with Virginia Tech engineering professor Linsey Marr for the journal Cell, Gandhi explained how cloth masks function. While the woven fabric is permeable, cotton fibers create a type of obstacle course, forcing pathogens to navigate around twists and turns. Many aerosols can't complete the journey, either colliding with or adhering to the fibers. This partial defense is enhanced by the surgical mask, which repels particles.
There are a few important notes. While surgical masks are effective for double-masking, it’s crucial they are made of polypropylene material. Gandhi advises that masks labeled as 'surgical' or 'medical' should meet the requirement.
Double-masking cannot replace an N95 mask, which filters out 95% of airborne particles, is primarily worn by healthcare professionals, and is most effective when fit-tested to ensure a proper face seal. Additionally, double-masking is not a substitute for adhering to current social distancing guidelines.
If double-masking is so effective, why are health experts recommending it only now? It’s not a new concept; mask filters have been suggested before. However, Gandhi explains that the push for double-masking now is due to the ongoing pandemic. “We always knew cloth masks weren’t perfect, but they were promoted for their acceptability and because previous surges were less severe,” she says. “Now, in the third and deadliest surge, with a lot of circulating virus, improving mask effectiveness can help reduce transmission rates while we wait for mass vaccination to end the pandemic.”
