The face covering debate has been raging for over a year now. Exactly how effective is one type over another at preventing the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, the virus that causes COVID-19)? Could cloth masks or face shields really prevent infection?
One study from the Health Effects Laboratory Division of the National Institute of Occupational Safety and Health1 compared N95 respirators, medical masks, 3-ply cotton cloth masks, polyester neck gaiters (single layer and folded into a double layer), and face shields. The study used fog to simulate respiratory droplets, and measured the percentage of emitted particles that penetrated the different mask types. As expected, the most effective was the N95, preventing 99% of their ≤7.0µm aerosolized particles from passing through. The medical mask prevented 59%, the 3-ply cotton mask 51%, and the neck gaiter 47% as a single layer and 60% as a double layer. Surprisingly, the face shield only prevented 2% of all aerosolized particles from spreading.
Another study released by the Physics of Fluid2 measured the spread of emitted particles from a person wearing different types of masks. The article supplied pictures and videos of their study showing emission of particles over time. Below are a few of those pictures:
Again, face shields appear to have little effectiveness when worn alone, though they can add a layer of protection to the wearer when combined with an appropriate cloth mask.
Cloth masks are far more effective than face shields at preventing the spread of aerosolized particles on the individual level. What about at the community level? The Centers for Disease Control and Prevention3 recognizes seven studies which analyzed the impact cloth mask wearing had on infection rates. All seven indicated significant reductions in infection rates after universal mask wearing directives were instituted by organizational and political leadership. Two studies, which analyzed SARS-CoV-2 statistics of 200 countries, showed a reduction in mortality rates as well. One study, conducted within the US, found that a 15% increase in mask wearing could prevent lockdowns and reduce economic losses of up to $1 trillion.
What does this mean for us? Wear a mask. Help prevent the spread of SARS-CoV-2. Cloth masks work. Whenever you travel within six feet of others in public, wear the best mask you have access to (cloth, surgical, or N95/KN95).
Note: Although face shields alone may not be as effective as cloth masks, studies have shown an even greater level of safety when worn in combination with a cloth mask.
For additional information, always consider the source. Keep to reputable websites, organizations, and scientific studies. There is a lot of information out there, including misinformation.
Remember, safety is everyone’s responsibility.
- Health Effects Laboratory Division – TF_Template_Word_Windows_2016 (medrxiv.org)
- Physics of Fluid- Visualizing droplet dispersal for face shields and masks with exhalation valves: Physics of Fluids: Vol 32, No 9 (scitation.org)
Centers for Disease Control and Prevention – Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2 | CDC