On April 3rd, the Center for Disease Control (CDC) recommended that all Americans wear cloth face coverings and subsequently followed up with more information regarding face coverings.
In this explainer, let’s break down why face coverings are needed, the differences between the various types of masks, and how to keep your masks clean.
Why wear masks and other face coverings?
For respiratory diseases such as COVID-19, there are two main routes of transmission: contact and inhalation of virus-containing droplets. Such droplets are let out when an infected individual coughs or sneezes, effectively releasing SARS-CoV-2 into the surroundings. The details following this first step of exposure to infection are covered in more detail in our Path of the Virus Explainer. The crucial point to know is that the viruses within these droplets can infect you through your mouth, nose, or eyes, and then move into your lungs.
This background is useful in understanding why masks matter. Specifically, masks lower your chance of exposure both by limiting the extent to which droplets get out into the air and by limiting the exposure of virus particles to your mouth and nose. Masks protect both you and those around you.
From the perspective of an infected individual, masks essentially capture the droplets and keep the virus from being released during coughs and sneezes. A person cannot spread the virus if their respiratory droplets are never released. This is especially important for asymptomatic individuals who do not actually know they carry the virus. One study used laser light to visually demonstrate the droplets released from talking with and without a mask—wearing masks dramatically decreased the number of droplets let out. Another observational study found that two infected hair stylists did not transmit the virus to any of their 67 masked clients.
For the non-infected person, wearing masks protects their mouth and nose, preventing the virus from ever getting in. This is why it’s critical to cover your nose and mouth when wearing a mask or any other face covering. Scenarios for the infected and non-infected individuals are depicted in the illustration below from a recently published paper.
As you can see in this figure, there is the least risk of transmission when both individuals are wearing a mask. You can also see how the droplets spread out and disperse more as they travel further from the speaker. This effect is magnified by airflow when we are outdoors, meaning that a smaller density of droplets (and virus particles) reaches the healthy person. Being outdoors with a mask on is one of the safest ways to interact with people. The figure also depicts that droplet size is an important consideration. The smallest droplets (smaller than 5 microns) are called aerosols, which can remain afloat for longer and travel further than respiratory droplets. SARS-CoV-2 can be transmitted via aerosols, but this is much less common and unlikely compared to transmission via respiratory droplets (it typically happens when an unmasked person is singing or breathing aggressively in an enclosed space).
What are the differences between the face coverings?
The most common face coverings are: 1) cloth coverings, 2) surgical masks, and 3) N95 respirators. The New York Times has an excellent interactive graphic comparing these types of masks.
Cloth coverings can be made of any common materials found at home such as scarves and shirts. The CDC has provided guidelines for home-made cloth coverings. Surgical masks are a loose-fitting type of personal protective equipment (PPE for short—you may have heard this term being used in the context of health care workers) that can filter some small particles such as viruses and also have some liquid penetration resistance. N95 respirators are another kind of PPE. They fit snugly around the face to cover any openings and provide liquid penetration resistance. Importantly, they maintain a more stringent filtration capability and are designed specifically to block small particles. The FDA provides a more thorough comparison of the different masks.
All masks differ in the degree with which they decrease risks of SARS-CoV-2 transmission. A recent study on surgical masks sampled emitted droplets from individuals without any form of face covering and from individuals wearing surgical masks. Researchers found that 3 of 10 (30%) of the respiratory droplet samples and 4 of 10 (40%) of the aerosol samples from those who weren’t wearing the masks contained SARS-CoV-2. However, when masks were worn, virus was not detected in any of the 10 droplet samples or in any of the 10 aerosol samples. Another recent study demonstrates that N95 respirators were even better at protection from infection than surgical masks for SARS-CoV-2. Both surgical masks and N95 respirators were more effective than multi-layer cotton masks.
A recent study from Duke used a device to track droplets expelled when a person speaks and tested 14 different types of face coverings. The study found that most cloth masks and surgical masks are the most effective in reducing droplet spread, and that neck gaiters and bandanas are relatively ineffective. Outside experts agree that a single layered neck gator or a bandana is not the most effective face covering but emphasize that these choices are likely better than wearing no mask at all.
In terms of cloth face coverings, one study demonstrated that higher threads per inch (TPI) cotton materials exhibited better filtration efficiencies. Researchers found that chiffon performs better than silk, which performs better than flannel. An important finding in the study is that multi-layering of different materials (such as one layer of cotton followed by a layer of silk) can dramatically improve filtration abilities.
Regardless of the specific face mask you use, it is critical to make sure it is worn correctly and that the nose and mouth are covered in order to maximize protection and reduce exposure to others.
Can I reuse my masks, and how do I wash them?
Currently, the CDC states that N95 respirators are not for use by the general public. This is because they are “critical supplies that must continue to be reserved for health care workers and other medical first responders.”
If you own surgical masks, it is important to note that they are designed for one-time use. The FDA states, “If your mask is damaged or soiled, or if breathing through the mask becomes difficult, you should remove the face mask, discard it safely, and replace it with a new one.” Washing surgical masks damages their filtration capabilities.
For cloth face coverings, the CDC has provided guidelines on how to wash them after use. In brief, you can wash cloth face coverings like regular laundry, though it’s recommended that the highest temperature settings are used for both washing and drying. Another option is to place the face covering in direct sunlight for drying.
How does wearing a mask affect my breathing during exercise?
A recent study found that when healthy subjects walked at 3.5 mph on a treadmill for an hour with and then without a mask, they experienced relatively small increases in heart and breathing rates and no differences in oxygen saturation. This means that a mask might make you feel slightly more out of breath if you are walking in one for an hour, but it is a difference that is “generally well-tolerated”.
However, breathing and heart rate are more significantly affected while performing intense physical activity in a mask. Surgical masks increase resistance to airflow, and since you breathe faster while exercising hard, you are rebreathing in recycled air. Many athletes report increased fatigue and lightheadedness when exercising in a mask. The WHO recommends not wearing a mask while exercising as it may reduce the ability to breathe comfortably and because sweat can make the mask wet, further increasing breathing difficulty while also promoting the growth of bacteria. However, the CDC recommends wearing masks in crowded public spaces such as parks or pathways. So, for some, wearing a mask might be the only way to feel safe while exercising. Several companies including Under Armour, Koral, and others have begun to manufacture masks intended for use during exercise.
Bottom Line
Wearing a mask reduces your risk of infection and the risk you transmit the virus to others. While N95 respirators are the most effective at preventing transmission, the studies highlighted in this article consistently show that the use of surgical and cotton masks can also greatly reduce the overall infection rate of respiratory diseases. This applies to people who are exposed both in health care settings and in general public areas. Mathematical models also confirm the impact wearing masks has in slowing the spread of the virus at the population level. The evidence is clear: face masks are an effective way to minimize exposure to COVID-19.