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Published: May, 2020; Vol 16, Num 12

 

How Effective Are Masks and Other Facial Coverings at Stopping Coronavirus?

One of the biggest areas of uncertainty during this ongoing pandemic has been over what seems like a relatively simple question: “What should I wear on my face to protect myself from getting COVID-19?”.

Answering that question requires understanding some key concepts about how the novel coronavirus (SARs-CoV-2) spreads and how various masks protect (and fall short) against those transmission methods. 

Understanding Particles, Droplets and Aerosols

We know SARs-CoV-2 is spread through respiratory droplets expelled by an infected person, such as during a cough or sneeze. Depending on the person and force of their breath, these droplets could be large enough to see (e.g., spittle during a hacking cough) or so tiny that they hang in the air and are invisible to the naked eye (e.g., during regular breathing).

Safety and health professionals have a term for these tiny particles that get suspended in the air – aerosols. The consensus is that SARs-CoV-2 particles can become aerosolized, which is critical to understanding how the virus spreads. That’s because gravity forces larger particles to the ground fairly quickly, but smaller, aerosolized particles can linger in the air for much longer. Being suspended in the air makes it much more likely for a virus to be breathed in, versus being on a surface and needing to be brought to our face by our hands.

The potential for airborne transmission – getting the virus from simply being in a room with an infected person for an extended period of time – is what’s driving the recommendations over masks and other facial coverings. So will any of these masks actually protect you from the virus?

Comparing N95s, Surgical Masks and Cloth Masks

First, let’s be clear that there’s no comparison between a correctly worn respirator, such as an N95, and other types of masks and facial coverings. Respirators are designed – and scientifically proven – to filter extremely small particles from the air. N95s and more protective options like elastomeric or half-face respirators are so effective because they form a tight seal to the wearer’s face, which forces all the inhaled air to pass through the filter.

Unfortunately, this is also why N95s are in such short supply. Knowing that it’s not realistic for everyone to wear an N95 respirator, let’s take a look at the potential benefits and limitations of other options in more detail.

Surgical Mask

Effective for: The primary purpose of these masks is to protect other people from the wearer’s respiratory droplets. These masks also give some barrier protection against larger respiratory droplets from other people.

Limitations: Because there’s no facial seal, surgical masks don’t reliably filter enough smaller airborne particles to count as respiratory protection. One study found surgical masks can filter about 60 percent of smaller, inhaled particles. (By comparison, an N95 would filter 95 percent of these particles.)

Paper Mask

Effective for: These masks are intended to filter larger nuisance dusts from the air, such as pollen or sawdust, which are much larger than virus particles. Like surgical masks, they provide some barrier protection for the wearer and those in close contact with the wearer.

Limitations: Though made of filtering material, they are not designed to filter inhaled particles as small as viruses and don’t form a face seal.

Homemade Cloth/Fabric Mask

Effective for: Homemade masks provide some barrier protection from large respiratory droplets expelled by other people. Perhaps most importantly, they reduce the spread of respiratory droplets emitted by the wearer. In one study, coughing through a cotton mask significantly reduced the amount of SARs-CoV-2 particles transferred to a test surface.

Limitations: As above, these masks don’t form a tight seal to the face and don’t reliably filter small inhaled particles. Attempts to measure the effectiveness of cloth masks to filter small particles show a wide range of results: cotton T-shirt (seven percent), shop towel (19 percent), coffee filter (49 percent). Material type and thickness (e.g., cotton, denim, canvas), fit to face (e.g., flexible nose bridge) and use of an internal filter (e.g., coffee filter) are just some of the variables that affected filtering efficiency.

Summarizing Available Mask Benefits and Limitations

The overall evidence shows that surgical masks, paper masks, cloth masks and other facial coverings all provide the wearer with some protection against SARs-CoV-2. Those benefits include a protective barrier for virus particles to land on instead of our mouth and nose, and a level of particle filtration (even though nothing comes close to an N95 respirator). In short, wearing a mask offers some protection against the virus, but there’s a big gap between some protection and effective protection.

While these alternative mask options are far from perfect, we should keep in mind that the biggest benefit of wearing them is likely for the people around you. We know small virus particles can hang in the air, and we know people can spread the virus without ever having symptoms. Any steps we can take to contain our coughs, sneezes and regular breaths behind a mask can help limit how far the virus travels. That alone is reason enough to put on a mask.

While homemade masks are far from a perfect level of protection, the reality is that slowing the spread of SARs-CoV-2 requires us to take advantage of every opportunity we have. We should also remember two other important points. First, no mask is a silver bullet. Even an N95 won’t protect you if you touch your face with contaminated hands right after taking it off. That’s why masks have to be used in combination with physical distancing, hand hygiene, cough etiquette and other precautions. Second, the reason we’re wearing homemade masks is so we can hopefully leave N95s and other more protective respirators for the healthcare workers and frontline workers who desperately need them.

[Nick Fox]