SciMoms COVID FAQs: Do masks slow the spread of COVID-19?

In this series of COVID FAQs, the SciMoms answer frequently asked questions about the coronavirus or COVID-19 pandemic. In this post, we focus on masks. Do masks slow the spread of COVID-19? Are masks dangerous? Should kids wear masks?

What are current mask recommendations in the US?

Photo by Adam Nieścioruk on Unsplash

CDC currently recommends that: “people wear cloth face coverings in public settings and when around people who don’t live in your household, especially when other social distancing measures are difficult to maintain.”

Take note of this last part – it does not say masks are only needed when distancing is difficult. You need a mask even when distancing is possible if you are interacting with people outside your household. Interacting is loosely defined as spending merely 1-2 minutes closer than 6 feet to someone.

It is critical to remember that masks do not make you invincible and should not provide an excuse to relax other preventative measures, like hand washing, distancing, not gathering indoors, and limiting interactions outside of your household.

These precautions are meant to be practiced together: wear a mask AND wash your hands AND watch your distance. On their own, the 3Ws (wear a mask, wash your hands, watch your distance) are not perfect. Each is like a slice of Swiss cheese. Alone, each precaution is imperfect, but when we layer them, we close more holes. In combination, these three practices can and have slowed the spread of COVID-19. 

Masks are not perfect but we know that practicing the 3Ws in combination can go a long way to slowing the spread of COVID-19.


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Do masks slow the spread of COVID-19?

Yes, wearing cloth face masks reduces transmissibility -— the chance of spread from an infected individual to a non-infected individual. While this is not a situation where a randomized controlled trial is appropriate, data from many types of studies together support this conclusion.

Who does a mask protect?

Wearing a mask directly protects others from you if you are infected. This also protects you by limiting the virus’ spread in your own community. Updated guidance from the CDC on November 10, 2020 indicates that masks also protect the wearer by reducing inhalation of virus-containing droplets. Data from the current pandemic suggest that spread has slowed in places with mask requirements and has continued to rise in those without. Wearing masks protects your entire community, including yourself.


Scientific Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2

What is the right way to wear a mask?

Your mask should cover your mouth and nose. It should fit snugly against the sides of your face without making it hard to breathe. 


How to Safely Wear and Take Off a Cloth Face Covering

How to wear a non-medical fabric mask safely

When should you wear a mask?

CDC recommends wearing a mask whenever you are around people outside of your household, especially if other physical distancing measures are hard to follow. Most disease transmission occurs through close interpersonal contact or droplet spread within 6 feet. Therefore, if you will have contact or interaction with anyone outside of your household, you should wear a mask. Practicing the 3Ws  when you have contact or interaction with anyone outside of your household can help to slow the spread of COVID-19.

If we all wear masks whenever we interact with people outside of our households without exception, we don’t have to worry as much about each other’s compliance in other situations. For example, if a friend does not wear a mask, you may have many questions about where they have been and who they have been with before deciding to get together. But if they wear a mask and practice the 3Ws in your interactions with them, you don’t need to be expending mental energy thinking about their behavior.

Wearing masks whenever you are out in public and interacting with people outside of your household is especially important given the relatively high level of transmission from people who don’t feel sick. Since some people are contagious even when they feel fine, we must wear masks even when you feel healthy (See previous FAQ on asymptomatic spread).


COVID-19: Considerations for Wearing Cloth Face Coverings

Should we be wearing masks outdoors?

The answer depends on whether you will be around other people: 

  • In your own backyard with your household only? No masks needed. 
  • In your own backyard with friends not in your household? Masks and very strict physical distancing.
  • In an empty park? No masks needed.
  • In a busy park? Masks.
  • Walking down a crowded street in a city? Masks.
  • Walking on a suburban street where you can stay more than 6 feet away from anyone you encounter? Have a mask on hand for when you cannot stay more than 6 feet away from people.
  • Exercising outside? Keep a mask on hand so you can wear one if you cannot stay more than 6 feet away from people.

The common thread here is people. Contact and interaction with other people provides paths for the virus to spread. We can cut off these paths by wearing a mask whenever we interact with people outside of our household.

A simple way to think about this is the two-thirds rule. If you can practice at least two of the three measures at any time, you can minimize the risk of getting or spreading COVID.

On April 27, 2021, CDC provided updated guidance for fully vaccinated individuals. This guidance recognizes the combined protection of vaccination and the relatively low risk of spread outdoors. This guidance lists specific outdoor situations where fully vaccinated people (and groups of people) can go without masks.

These updates have been summarized by Drs. Steier and Love from Unbiased Science Podcast.

Those who are fully vaccinated can go maskless in the following outdoor situations:

  1. When you are exercising or enjoying the outdoors with members of your immediate household.
  2. When you are attending a small outdoor gathering with fully vaccinated family and friends.
  3. When you are attending a small outdoor gathering with a mix of vaccinated and unvaccinated family and friends.
  4. When you are dining outdoors with friends from multiple households.

If you are participating in outdoor activities that have crowds such as parades, sporting events, performances, etc., fully vaccinated individuals should continue to wear masks.

For those who are unvaccinated, it is low risk to go maskless in the following outdoor situations:

  1. When you are exercising or enjoying the outdoors with members of your immediate household.
  2. When you are attending a small outdoor gathering with fully vaccinated family and friends.

However, you should continue to wear a mask during these situations:

  1. When you are attending a small outdoor gathering with a mix of vaccinated and unvaccinated family and friends.
  2. When you are dining outdoors with friends from multiple households.
  3. When attending a large, crowded, outdoor such as described above.

These last two activities are much higher risk for those who are unvaccinated, so mitigation measures such as mask wearing are very important to reduce the spread of the virus.

This specific question was updated on April 27, 2021 based on new CDC guidance for fully vaccinated people and wearing masks outdoors.


Choosing Safer Activities

Are there any reasons why someone should not wear a mask?

According to CDC, there are a few exceptions to this guidance. The following people should not wear a mask: children under 2, anyone who has trouble breathing, is unconscious, incapacitated, or otherwise unable to remove the mask without assistance.

Do not wear a mask when engaged in activities that get the mask wet, like swimming at the beach or the pool. When swimming, it is particularly important to maintain a distance of greater than 6 feet from people outside your household.

CDC recommends adaptations and alternatives to make it easier to wear a cloth face covering in situations where wearing masks may be difficult.

  • People who are deaf or hard of hearing, or who interact with those who are deaf or hard of hearing, can consider a clear face covering to allow for lip reading.
  • People with intellectual and developmental disabilities, mental health conditions, or sensory sensitivities should consult with their healthcare advisor for specific advice about wearing face coverings.
  • Young children (preschool and early elementary aged) may have trouble wearing a cloth face covering for a prolonged period of time. Use should be prioritized for times when it is difficult to maintain a distance of greater than 6 feet from others.
  • If wearing a mask is difficult when engaged in high intensity activities (like running), conduct the activity outdoors or in a place with good ventilation and where it is possible to maintain greater than 6 feet from others.
  • Wearing a cloth face covering in certain work settings can cause safety concerns (heat-related illnesses or straps getting caught in machinery). Occupational safety and health professionals can help determine appropriate face coverings in these situations.


Considerations for Wearing Cloth Face Coverings: Feasibility and Adaptations

Should kids wear masks?

Kids over the age of 2 should also wear masks over their mouths and noses while in public. Kids can get COVID, with some developing serious complications. Kids are also able to spread the virus to others. Even though they are not in a high-risk category and there is some data suggesting that younger children transmit the disease at a lower rate, kids can still get sick and spread the virus. Therefore, it is important for kids to also practice the 3Ws.

The Action Learning Network has published tips for helping kids get used to wearing masks. You can visit their website to find this and additional graphics in English and Spanish.

Tips include:

  • Let them pick out a mask they like for both fabric and fit. Let them decorate their mask as long as the decorations don’t interfere with breathing.
  • Practice wearing the mask at home to help them get used to it.
  • Model proper mask wearing. Wear your mask whenever you are in public and ask them to do the same. Wear your mask over your mouth and nose.
  • Make play masks for stuffed animals and dolls.


Help Stop the Spread of COVID-19 in Children

COVID-19 — Action Learning Network

Is wearing a mask dangerous?

No. Surgical and cloth masks do not lead to oxygen deprivation or CO2 intoxication, as some people on the internet have claimed. Doctors wear masks for many hours at a time with no ill effects. They may be uncomfortable and take some getting used to, but they are not dangerous. Note that there are individuals who should not wear masks (See question above for exceptions to mask recommendations).

Going out without a mask endangers you and your community. If you choose not to wear a mask, you should be more diligent about physical distancing practices and should choose to utilize services like curbside pickup. 


Is It Dangerous to Wear a COVID-19 Protective Mask for Too Long?

What is the difference between respirators, N95s, KN95s, surgical masks and cloth masks?

The CDC recommendation above is for cloth masks and cloth face coverings. These are different from surgical masks or respirators (N95s). Surgical masks and N95 respirators are considered critical supplies that must be reserved for healthcare workers, medical first responders and other professions that require them.

N95s are respirators, not masks. When fitted and worn properly, they remove particles, like bacteria and viruses, from the air before you breathe it in. These fit tightly and reduce the wearer’s exposure to airborne particles. N95s must be approved by the National Institute of Occupational Safety and Health (NIOSH) to ensure that they work properly.

KN95s are also respirators, but are not NIOSH-approved. These are regulated by the Chinese government. Normally, these are not allowed to substitute for N95 masks in the US. However, in April 2020, FDA authorized use of KN95 masks as an alternative because of shortages of N95s.

Surgical masks are loose-fitting masks that prevent the wearer from spreading droplets to others and to surfaces.

Cloth face masks are not used by professionals and should be worn by the general public. Like surgical masks, they prevent the wearer from spreading droplets to others and to surfaces. Wearing masks whenever you interact with people outside of your household will help keep people who do not know they have the virus from transmitting it to others. Wearing masks in public places can also prevent you from depositing viruses on shared surfaces, which may play a role in transmission (See previous FAQ on spread and transmission by fomites).


Infographic – Understanding the Difference, Surgical Mask, N95 Respirator

Coronavirus Face Masks: Types & When to Use

What type of cloth mask is best?

A recent study tested many dozens of fabric types and found that tight-weave 100% cotton is the best option. What does tight-weave mean? The NPR article linked in resources suggests holding the fabric up to a light: “If you can easily see the outline of the individual fibers, it’s not going to make a great filter.” In this study, most synthetic fabrics were not as good as tight-weave 100% cotton, but 100% polyester performed well. However, even a synthetic mask is better than no mask. 

A new study published in Science Advances on August 7, 2020 reported a low-cost method of measuring how well masks filter expelled droplets. To demonstrate how their setup works, they tested 14 different actual masks. While this is a very small study intended to demonstrate the utility of their setup and method, it was massively misreported in the media as demonstrating that neck gaiters and bandanas were no better than no mask. A single layer “knitted” mask performed only slightly better. (Visit the link above for photos and descriptions of the masks tested.) Other types of masks were able to filter to varying degrees in this particular test. Consistent with previous studies, the best 4 performing masks were multiple layers and cotton and/or polyester. In short, this study reports a potential cheap way to test mask efficacy but doesn’t really change what we already know.

  • Two, or even three, layers of fabric are better than a single layer.
  • A mask with two layers with a filter in between is even better and is still breathable.
  • Filters made of polypropylene are ideal but, if you can’t find polypropylene filters, scientists recommend using 2 layers of tissue in place of a filter or using a 3 layer mask without a filter.
  • Even if you don’t have a filter, a mask without a filter is still better than nothing.
  • Bandanas and gaiters might be less effective at blocking the spread of droplets because they are not well fitted around the mouth and nose.
  • Do not use masks with exhalation valves. These let out unfiltered air which defeats the purpose of a mask.
  • A mask must fit well to filter out particles. Make sure your mask covers your mouth and nose tightly without gaps at the sides. A mask does not need to cover your chin, but it is easier to get a good fit around your both if it is snug around your chin.
  • Any face covering is likely better than no face covering.


Dear Pandemic: Some cloth masks have a pocket to insert a filter, is this necessary? If so, what material is best for the filter?

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Filtration Efficiencies of Nanoscale Aerosol by Cloth Mask Materials Used to Slow the Spread of SARS CoV-2

Household Materials Selection for Homemade Cloth Face Coverings and Their Filtration Efficiency Enhancement with Triboelectric Charging

Low-cost measurement of facemask efficacy for filtering expelled droplets during speech

Discussion of what the above study means from Your Local Epidemiologist on Facebook

Save the Gaiters!

Should you wash your mask?

Cloth masks should be washed after each use with soap or detergent in hot water. Allow the mask to completely dry before you reuse it. 

However, washing your mask daily may not be practical and could shorten the life of your mask. Frequency of washing depends on how many masks you have available, how long you are wearing them, and how dirty they are. If you have to wear a mask all day for your job or school, your mask may be pretty gross by the end of the day and need cleaning. But if you only wear it for an hour each day to go pick up groceries, then you may be able to rotate your masks and wash less frequently. James Hamblin at The Atlantic answers this question in detail here, but this is the take home message.

“Have several masks, made to fit well around your nose and mouth. Make them as heavily layered as you can tolerate. After wearing them for a day or so, or in a high-contact scenario, let them sit for a few days in a sunny, out-of-the-way place. Between the effects of time and light, there should be little need for running a washing machine or going through the hassle of hand-washing your masks. Well, unless they just smell terrible.”


How Should I Wash My Cloth Mask?

How to Wash a Cloth Face Covering

Why has advice on masks changed?

The advice on masks has changed due to a combination of factors. Some of these include shortages of critical supplies, a communication failure by public health officials, and increased community spread due to a failure to implement the appropriate mitigation strategies.

Official statements have claimed this is due to increasing evidence of asymptomatic spread, but scientists have suspected there was asymptomatic spread since very early in the pandemic (See previous FAQ on asymptomatic spread). What has changed is the situation in our communities. The situation has changed dramatically since early March, when the first lockdowns went into effect.

PPE shortages

Early in March, there were widespread shortages of N95 respirators and surgical masks for health care workers. People were hoarding supplies to gouge the market. In addition, the National Stockpile was not adequately prepared to supply needed PPE. As a result, these shortages endangered healthcare workers in some of the hardest-hit areas of the country.

Based on that situation, communications from health agencies focused mainly on these critical supplies because of these shortages. The official advice about masks at that time was mainly referring to N95 respirators and surgical masks but, by the time this information made its way to the public, the message became that the general public doesn’t need masks of any type. 

Yet the core piece of this recommendation has never changed, even with the newest mask guidance. The general public should wear cloth face coverings. The general public should also reserve N95 respirators and surgical masks for the health care professionals who need them.

A False Sense of Security

There was also a reluctance to recommend masks in case it gave people a false sense of security, leading them to relax the other measures. The 3Ws are: wear masks AND wash hands AND watch your distance. It is always better to stay home and only go out when necessary. It is always better to only interact with those in your household. Wearing a mask reduces the risk of transmission when you must interact with people outside your household, but should not be seen as a permission slip to relax other precautions. While I have not seen data on whether this effect is true, anecdotally, I see this all around me. Wearing a mask should be done in combination with washing your hands, watching your distance, and not gathering indoors.

Widespread Community Spread

Another critical piece underlying this policy change is that the pandemic is far worse now than it was back in early 2020. Widespread face coverings are not needed if community spread is limited. Some countries like Iceland and New Zealand were able to implement effective lockdowns, adequate testing, and contact tracing programs early in the pandemic to control the spread without requiring widespread mask-wearing. If we had adhered to strict lockdowns and used that time to implement appropriate testing and contact tracing programs, we might not have reached the point in the pandemic where masks are needed. 

What happened instead is that most areas of the US have largely failed to contain the virus. In fact, part of the reason we now need masks is that we reopened too early and too quickly. As a result, the percentage of the population who are spreading the virus is now exponentially higher than it was in March. The sickening irony is that those who pushed to re-open early are also the people now resisting wearing masks. Because of our failures to control the spread of the virus early on, we are now at a point when masks are necessary to help control disease spread. 

Scientific uncertainty

Science is a process, not a body of knowledge. However, we largely teach and report science as if it were static and fixed. Knowledge and consensus are built by this process and it’s messy: the back and forth, the confusion, the conflicting evidence. This is normal for the scientific process, but the process is not usually this visible to the general public. 

With the pandemic, the public is seeing how this process plays out in real-time and it is jarring to those who aren’t used to the fits and starts. Part of the change in mask guidance is the scientific process playing out in real-time.

All of these issues were overlaid with a great deal of scientific uncertainty regarding the effectiveness of cloth masks. The studies that existed did not provide conclusive evidence about whether cloth face coverings worked or not, so that added another layer of confusion.

Policy is shaped not only by science, but also by culture and economics. Given the lack of conclusive scientific evidence, perhaps too much deference was given to cultural factors that make Americans resistant to wearing a mask and not enough consideration was given to cloth masks early in the pandemic.

At this point, the evidence that we have clearly supports wearing a mask to slow the spread of COVID-19. Masks alone are not a silver bullet that will stop this pandemic in its tracks. But in combination with physical distancing, hygiene, limited interactions outside your household, and not gathering indoors, masks are a cheap, low-risk, and science-based measure that can help us resume some sense of normalcy in our lives.


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