Wearing a Mask During Coronavirus—Separating Myths from Facts

We have scientific evidence that masks effectively and dramatically reduce the spread of COVID-19, yet myths about mask-wearing abound. Let's put them to rest and mask up!

Sabrina Stierwalt, PhD
7-minute read
Episode #381
The Quick And Dirty

Science shows that wearing masks—even simple cloth ones—prevents viral spread. Here are the facts:

  • Mask-wearing prevents the spread of infected viral droplets that are produced not only by sneezing and coughing but also by talking and simply breathing.
  • Countries where mask-wearing is more of a cultural norm show lower death rates.
  • People can spread COVID-19 while asymptomatic or pre-symptomatic. Even healthy people should wear masks.
  • Although masks are more beneficial for keeping you from spreading the virus to people around you, there are benefits to mask wearers, too.
  • Experts recommend wearing a mask in public even when you're social distancing.
  • There's no evidence to support that mask-wearing causes a toxic buildup of carbon dioxide (hypercapnia).
  • Simulations of viral spread show that if 80 percent of the population wore masks that were 60 percent effective, the virus would die out.

As scientists work overtime to learn about the novel coronavirus SARS-CoV-2 and how to fight it, our latest understanding of the virus constantly changes. Our understanding of mask-wearing is no exception. Let's dispel some myths.

MYTH: We don't actually know if masks can prevent the spread of COVID-19.

The more we learn about the virus and how it's spread, the more evidence we find to support the benefits of wearing a mask. 

When we talk, we produce oral fluid droplets—a fancy word for spit—that can carry viral particles capable of infecting others. These droplets come in a range of sizes and the smaller droplets can travel further because they're lighter. One group measured just how far by highlighting the paths of spittle with lasers and high-speed video. (Check out their video if you want to be simultaneously amazed and grossed out.) They saw that speaking just one phrase—“stay healthy”—generated droplets as small as 20 microns and as large as 500 microns in size. But when the speaker placed a damp washcloth over their mouth, none of those droplets made it through. 

Countries where mask-wearing is more of a cultural norm show lower death rates.

There's also some evidence to suggest that the same amount of droplets are produced when talking as when sneezing or coughing, activities we more commonly associate with viral spread. The evidence also shows that those speaking-generated droplets are smaller, which makes them capable of further spread. 

But some epidemiologists argue that the strongest evidence for the importance of masks is looking at overall case counts in places where people wear masks versus places where people don’t. Countries where mask-wearing is more of a cultural norm show lower death rates. The increase in coronavirus cases in Washington, D.C. slowed noticeably after a mask mandate was put in place. 

There are also studies of individual events where masks clearly prevented transmission. For example, two hairstylists in Missouri saw 140 clients while they were infected with COVID-19 and thus likely contagious, but not a single client tested positive. Everyone had been wearing a mask. 

MYTH: The mask advice keeps changing, so it’s just going to change again. If I’m not sick, I don’t need to wear a mask. 

The origins of this myth are easy to understand. The World Health Organization (WHO) and the Centers for Disease Control (CDC) both recommend wearing masks to slow the spread of the virus, and masks are mandated in several states and countries. But this wasn’t always the case. In fact, in the US we were first told the opposite. So now some wonder why they should bother with the inconvenience of a mask when it doesn’t seem like the health experts are even sure they help.

As we’ve just seen, there's no doubt that wearing even a cloth mask can substantially slow the spread of the virus because it helps you keep your spittle droplets to yourself. What has changed since the start of the pandemic is our understanding of how important it is to control those droplets. Epidemiologists and infectious disease experts at the University of California San Francisco, one of the leading research hospitals in the United States, note a few reasons for this shift. 

Not only can you be infected without knowing it, but you can also pass the virus onto someone else who may suffer far more dire consequences.

First, we now know that asymptomatic spread is playing a role in spreading the virus. This means that not only can you be infected without knowing it, but you can also pass the virus onto someone else who may suffer far more dire consequences. Back when we thought only those with symptoms were spreading the virus, masks seemed less necessary since hopefully, those symptomatic people were staying home until they felt better.

Just how prevalent is asymptomatic spread? We still don’t know the answer to that, but researchers are getting close. Individual studies have given a huge range of results. A cruise ship in Japan found 18 percent of passengers that tested positive for the virus were asymptomatic. A study of over 3,000 inmates who tested positive for coronavirus in four prisons in the United States found that 96 percent of those patients were asymptomatic. 

But now our database of coronavirus cases is large enough that researchers can begin to sample across populations. Those samples include people of different ages and with different pre-existing conditions, including prior exposure to disease. A trend is starting to emerge. One investigation that combined data from over a dozen literature studies found that between 30-45 percent of those infected with the virus do not show symptoms. Of course, that means they may not even know they have it.

It’s worth noting that, when it comes to COVID-19, asymptomatic doesn’t mean unaffected. Growing evidence shows that those who contract the virus and show no obvious symptoms may still face long-term health effects. Asymptomatic COVID-19 patients have shown haziness in their lungs and even brain disorders

A second related reason for the change in mask messaging is the possibility of pre-symptomatic spread of the virus. We now know that you can spread the virus before you show any symptoms yourself. In fact, peak transmissibility—the period of time when you are most contagious—may even be 1-2 days before you show any symptoms. One study published in Nature Medicine estimated that 44 percent of patients who contracted the virus got it from someone who was pre-symptomatic. 

Finally, a third reason we in the US may have been told that we did not need to wear masks at the beginning of the pandemic was the critical shortage of personal protective equipment (PPE) in our hospitals. Given the consumer-driven panic in the early days of the pandemic that led to grocery shelves cleared of toilet paper and bleach, public health experts feared that a run on the market for medical-grade masks would leave hospitals in even more dire need. 

MYTH: A mask only helps others, not me

Let’s assume that you don’t need to be convinced to care about your friends and neighbors and look at this question from a purely science-driven angle. Who does a mask protect? 

Non-medical grade facemasks, including cloth masks and bandanas, are most effective at trapping your own spittle droplets and thus protecting those around you should you be carrying a virus. They are not a filter small enough to refuse entry to microscopic viral particles and they also don’t cover your eyes, another possible entry point for the virus.

Health experts make it clear that we should not bask in a false sense of security when wearing a mask. But there are benefits to the wearer.

So health experts make it clear that we should not bask in a false sense of security when wearing a mask. But there are benefits to the wearer. For example, it’s not always possible to stay six feet apart, like when buying groceries or on public transportation. If someone were to sneeze on me, I know I’d feel better having some barrier between us rather than nothing. If you have a well-fitting mask that you don’t constantly adjust, facemasks can also remind you not to touch your face. 

Perhaps most importantly, reducing the spread of the coronavirus ultimately protects all of us by reducing our chances of encountering the virus when we go out. It’s a no-brainer that the fewer people who have the virus, the better for all of us. 

MYTH: I don’t need to wear a mask if I’m social distancing

Experts still recommend wearing a mask, even when social distancing. We see far more evidence of the virus being passed through respiratory droplets, and thus contact with other people, than we do via contact with surfaces. So if you’re wiping down your groceries or watching what you touch outside your house, you should definitely also be wearing a mask. 

MYTH: Masks create a toxic buildup of CO2

And let’s dispel the myth that you will somehow pass out from breathing in too much of the carbon dioxide you exhale behind your mask.

For those looking for an excuse not to wear a mask, this claim of the risk of hypercapnia—toxic levels of carbon dioxide in the blood—seems reasonable. But there is no evidence to support it.

For those looking for an excuse not to wear a mask, this claim of the risk of hypercapnia—toxic levels of carbon dioxide in the blood—seems reasonable. But there is no evidence to support it. Most masks worn by the public are not airtight and thus can’t effectively trap enough carbon dioxide to affect the wearer.

And now, let's think logically about the fact that surgeons and other medical workers and caregivers wear masks all the time. Their masks are far more constrictive than the ones the rest of us wear. Not only that, but medical workers wear their masks for long stretches of time. They don't experience hypercapnia. One study of nurses during the SARS epidemic in 2006 found that healthcare workers wearing N95 masks for long stretches experienced headaches, which the CDC notes would likely occur before any dizziness.

Chronic obstructive pulmonary disease (COPD) and sleep apnea both can cause hypercapnia, so if you have one of these conditions and are concerned about mask-wearing, consult your doctor. 

Simulations of viral spread have shown that if 80 percent of the population wore masks that were just partially (60 percent) effective—like a cloth mask worn with a minimal amount of fussing with it—then the reproduction rate of the virus (called its R-value) would drop below one, meaning the disease would die out. Other simulations show that if 80 percent of the population wore masks, the result would be more of a reduction in the virus than a complete, strict lockdown. I know I'd pick a small face covering over a lockdown any day. 

Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.