How Simple Face Coverings Protect Against COVID-19
In this Q&A, two physicians discuss why cloth face coverings provide value, even though they are not considered personal protective equipment.
In the current pandemic, the wearing of masks or improvised facial coverings is mandated in most public locations in an effort to reduce the spread of the respiratory coronavirus 2019 (COVID-19).
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Medical-grade masks such as the N95 are known to provide the best protection against breath-borne pathogens. With such masks in short supply, the general public has resorted to wearing homemade masks or improvised masks made from scarves or bandanas.
“Cloth face coverings are intended to keep the wearer from spreading respiratory secretions when talking, sneezing or coughing,” says Steven Gordon, MD, Chairman of Cleveland Clinic’s Department of Infectious Disease. “Cloth face coverings are not personal protective equipment, and it is uncertain whether they protect the wearer.”
Nevertheless, cloth face coverings can be effective and do have a place. We asked Dr. Gordon and pulmonologist Raed Dweik, MD, Chairman of Cleveland Clinic’s Respiratory Institute to explain the scientific justification for wearing simple masks that Dr. Dweik and three colleagues recently published in the Journal of Breath Research.
The public fears that loose-fitting masks and those made of permeable materials such as cotton, do not prevent viral particles from being inhaled. Are they correct?
Dweik: Yes, in a sense. However, there is evidence that such masks reduce the exhaled aerosols from infectious, but asymptomatic, individuals. This reduces the viral load in the environment, lowering the chance that anyone will inhale the pathogens.
Moreover, coughing and sneezing significantly increase the amount of aerosols in an exhaled breath, creating a turbulent cloud that can propel the contents up to 25 to 26 feet. Any type of facemask provides a physical barrier that disrupts this event.
How do we know that non-medical-grade masks stop viral particles from being exhaled into the surrounding air?
Dweik: Our normal exhaled breath is comprised of tiny water droplets and fluid from the lining of the lungs that carries dissolved bacteria, viruses, proteins, metabolites and other compounds. As they enter the air, the aerosols begin to dry and, ultimately, only the dissolved materials remain.
Even though exhaled breath may leak around a face covering that does not fit snugly, two recent journal articles illustrate that the exhaled aerosols and particles collect on the inner surface of the face covering and form a layer that attracts more particles. The studies were performed on masks long after they had dried, confirming that the contents remained attached to the surfaces after the wet layer had evaporated.
What is the evidence that improvised facial coverings trap the coronavirus?
Dweik: Both studies found a wide variety of endogenous human materials on the disposable masks, including human cytokines. These proteins are much smaller than virions from the coronavirus. If masks made of paper, cotton and other homemade masks are capturing the smaller molecules, it is reasonable to assume they are also capturing the larger SARS-CoV-2 particles.
How do cloth masks fit into return-to-work practices as we move from sheltering in place to recovery in the COVID-19 pandemic?
Gordon: Cloth face coverings can be used for source control in the workplace as well as in public spaces. They are recommended by the Centers for Disease Control and Prevention (CDC) to potentially help prevent transmission when used as a complement to social distancing. They are not a replacement for adequate distancing, and their use and facility should be reconsidered when distancing is not feasible. The CDC offers guidance on the design, use and maintenance of cloth face coverings.
Dr. Dweik reinforces that medical-grade masks are ideal because they fit snugly on the face and force breath through the material to filter aerosols being inhaled and exhaled. However, when these masks are not available, surgical masks and homemade face coverings still have value. “While they may not protect the wearer from inhaling contaminants such as the coronarvirus, they appear to reduce the viral load exhaled from an asymptomatic wearer,” he says.
“Therefore, wearing a face covering helps protect others from the wearer’s exhaled aerosols, but does not protect the wearer.”