Face Mask Effectiveness Against Coronavirus

Closeup of various face masks on a table, from cloth and disposable masks to KN95 and N95 FFP masks.

The CDC officially updated its recommendations in April suggesting that all Americans wear a mask when they go out in public. More recently, states such as California has mandated that all persons must wear face coverings while out in public. But still, there have been numerous debates about face mask effectiveness.

Some people have taken the stance that face masks won’t protect them from getting the virus. Masks are merely an annoyance that won’t help. Others have stressed that masks are important because they slow down the spread of the virus by making it harder for it to transmit from person to person.

So which is it?


Group of three (all wearing masks) in a restaurant, being served by a waiter (also wearing a mask).
It’s important to wear a mask in public, even at a restaurant.

The reality is that your mask is meant to prevent you from sharing the virus with people around you. Other people wearing a mask is meant to protect you from catching it from them. That’s because the virus spreads through tiny droplets, many of which can get stopped by a standard cloth mask. However, the mask is only one part of COVID-19 precautions along with social distancing and hand washing. It’s effective in many ways, but it isn’t infallible.

Mask Effectiveness: The Evidence

To date, we have a lot of evidence showing the effectiveness of masks. Some of it is lab-based, whereas a lot come from real-world scenarios.

A lot of lab studies dealt with respiratory droplets and the ability of various masks to block them. The high-speed video of one such experiment showed hundreds of droplets were generated when saying a simple phrase. These droplets ranged between 20 to 500 micrometers. Nearly all droplets were blocked when the mouth was covered by a damp washcloth.

Another study of people who had influenza or the common cold found that wearing a surgical mask was extremely effective in reducing the amount of the virus emitted in droplets (or aerosols).

Nurse wearing gloves, gown, face mask and face shield administering a swab COVID test.
Nurse administering a swab COVID test.

A recent study published in Health Affairs, for example, compared the COVID-19 growth rate before and after mask mandates in 15 states. The findings were conclusive: Mask mandates led to a slowdown in daily COVID-19 growth rate. Over time, that slowdown became apparent over time. The daily growth rate slowed by 0.9 percentage-points compared to the five days prior to the mandate. At three weeks, the daily growth rate had slowed by 2 percentage-points.

Why Masks Help Slow the Virus Spread

If you’ve been paying attention to the news about COVID-19, you might have noticed that it’s common for young, healthy people who have the virus to show mild or even no symptoms. Given that tests are expensive and not as widely available as they should be, many Americans haven’t been tested for the virus, meaning that it’s a guessing game as to how many people have contracted the virus.

Wearing a mask makes a difference because it helps prevent you from spreading the virus to others if you’ve contracted COVID-19 and don’t know it. When you cough or sneeze, you send tiny droplets flying through the air at high speeds, which allows them to land on another person or an object. Once they’ve landed, any virus contained within them must find a host in order to survive. If it doesn’t, it quickly dies out.

A man and woman, both wearing masks and gloves, on talking to each other on mass transit.
Wearing a mask along with other PPE helps protect you from spreading Coronavirus.

That’s why hand sanitizer, soap and protective gloves work in conjunction with a mask. All of those tools are meant to either stop the virus from landing on skin or kill it once it does land on skin. If you’re in a situation where you can’t wash your hands or use hand sanitizer, your mask offers a final layer of protection. It makes it harder for the virus to access your nose and mouth. The virus needs inside your body to gain access to your cells, and covering your nose and mouth with an effective mask deprives it of two of the easiest entrances. It’s a simple task that goes a long way in limiting the spread of the virus, making it easier for us to beat this disease.

Why Medical Professionals Wear Different Masks

If you’ve been in a well-staffed hospital, you might have noticed that some nurses and doctors have personal protective equipment, such as N95 respirators and the functionally equivalent KN95 masks. These are saved for medical staff because they’re in constant contact with the virus and need equipment more effective against air-borne pathogens.

Instead, nurses and doctors use a respirator that filters the air around them, preventing virus particles from ever entering their bodies. When they breathe in the air from around a sick patient, their filter prevents the disease from entering through their nose or mouth, letting them continue to fight the virus.

These masks aren’t common in everyday life because there’s only a limited supply of them, and we need to make sure that our medical experts are ready to do their best to fight COVID-19 and help us do the same. For the rest of us, masks and social distancing will go a long way toward limiting the spread.

Why Aren’t Cloth Face Masks 100% Effective?

Face masks work to filter out particulates, which are very small. N95 and KN95 masks can filter out 95% of particulates as small as 0.3 microns. That’s small! Pollen particles, for example, are often 10 microns or bigger. Bacteria are often about 1 micron. The coronavirus has a diameter of approximately 1.4 microns. Most cloth material simply cannot block that small of a particulate at close range. By “close range” we’re talking around 16.5 cm, as in this experiment. Studies of cloth masks when proper physical distancing is in place shows much better aerosol blockage.

Remember, the mask is meant to keep things from getting out, not from coming in. If you’re wearing a mask, you might be protecting others if you have the coronavirus, but you still need to practice proper social distancing and shelter in place if you’re able to do so.

“Putting a face mask on does not mean that you stop the other practices,” said May Chu, a clinical professor in epidemiology at the Colorado School of Public Health — University of Colorado. “It does not mean [that] you get closer to people. It does not mean [that] you don’t have to wash your hands as often and you can touch your face. All of that still is in place, this is just an add-on.”

The most important thing to remember about face mask effectiveness is that face masks are meant to work in conjunction with other recommendations from the CDC. Think of a mask like you would the wheels on your car. They’re critical from helping you get from place to place, but their useless without other parts of the car. Be smart. Wash your hands frequently. And keep practicing physical distancing while you’re out and about.

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