13. Masking for Public Health

Everything you wanted to know about masks (but were afraid to ask)

Millions of children across the United States are returning to school this week. School bags are packed. Notebooks have been cleaned out, and for many, a new type of mask will be worn. It can be confusing to figure out which mask works best for you.

This article is meant to help you make a more informed decision.

How is Covid-19 Transmitted?

It is important to first talk about how Covid is transmitted, and why it continues to be a global problem. Omicron is here, and it’s a version of Covid that is even easier to catch.

Covid is passed from one person to another person in tiny droplets that come from your mouth and nose. This happens when we speak, sing, cough, sneeze, eat, or any number of other common activities. These droplets can float in the air for a while - no one knows for sure, but they probably drift in the air for several minutes to as much as a few hours. That means these little infection bombs can float in the air across a lengthy distance.

Unfortunately, this means when an infected individual is present in a room, everyone else can be at risk. When these droplets make their way to you or I, we inhale them into our lungs with each breath, and this can lead to an infection.

At the beginning of the pandemic, scientists assumed that these little droplets were actually bigger droplets, and fell out of the air rather quickly. This is where the six foot (and later three foot) social distancing recommendations come from, because big droplets fall to the ground quickly.

We now know much more about Covid - these droplets are smaller and lighter, and as a result, can float well beyond this 6- or 3-foot distance.

Covid itself is only about 125 nanometers, which is microscopic and impossible to see with your naked eye. However, it usually catches a ride inside of bigger droplets - usually 200-100,000 nanometers that are exhaled from your mouth and nose. The largest of these particles are pretty easy to capture with any mask. But those smaller ones are tricky to catch. And when we breathe or cough or sing, all sorts of different sized droplets are released.

To give you an idea of how small 200 nanometers is: you’d need to stack about 400 of them on top of one another to have something as tall as the thickness of a single strand of human hair.

Masks have never been more important, especially with these newer Covid variants. They aren’t perfect, but it’s our best shot to keep people - like school kids, transit riders, and people who interact with other people for a living - safe.

How do Masks Work?

There are a wide range of masks available to the consumer, with confusing names and certifications. Here, I use the term ‘masks’ to describe the range of face coverings we see on a daily basis. Strictly speaking, the term ‘mask’ refers to the cloth ones or the pleated surgical masks that are commonly worn. N95 face coverings, which I talk about later, are technically known as ‘respirators’. But here, I use the term mask interchangeably because it makes it a little easier to understand.

Image: Peltier Aerosol Lab, University of Massachusetts Amherst

Masks work simply by filtering droplets and particles from the air. This includes filtering these droplets that pass through the mask to the wearer, but also by filtering the droplets that a mask-wearer emits. But the best ones work when there is a close, air-tight fit around the edges of the mask to your face. And this is the hardest part to achieve.

Personally, I alternate between different types of masks based on what I think my risk might be. But I know the science - it’s what I do. Let me help you understand this a little better. And if there is a question that I don’t address, please leave a comment. I am unable to respond to questions about specific makes or models of masks, however.

Certified masks

Certified masks are those that have been evaluated by government safety agencies and are usually approved by that agency. There are many different types of certified masks that can make it very confusing - N95, KN95, KF94, P2, FFP2, FFP3 and so on. The different codes refer to the different standards in other countries. In the US, it’s N95. In Korea, it’s KF94. China certifies masks as KN95, P2 for Australia, and FFP2 and FFP3 are European Union standards. And there are a few others, too.

While there are some differences between the different types of certified masks and how they are tested, they all work pretty much the same as one another. But very few nations officially recognize masks that comply with other national standards. So while you can buy a KN95 or KF94 mask in the United States, it isn’t formally approved for use as a safety device by US government agencies. You’d need a N95 mask for that. But for the most part, KN95 and KF94 masks work about the same as a N95 mask - they both protect the wearer. The same is true for most of the other certified masks out there.

But no matter your choice, these certified masks have a number of important advantages. Certified masks are designed to form a tight seal against your skin, and this prevents leaks into the mask, but they also prevent leaks out of the mask. They are made of specialized fabric that is specifically designed to catch the smallest droplets - again, both into the mask and out of the mask - and it captures even smallest ones, particularly for the sizes that might carry Covid.

These are the trickiest droplets to catch. but certified masks do a very good job at capturing them. And because they can also fit very well to an individual’s face, they protect both the person wearing the mask, and they keep others safe.

Strengths of Certified Masks

1. These masks are effective at capturing all sizes of droplets. And they capture both droplets that are exhaled by the wearer, and droplets that might be inhaled from your environment.

2. They fit tightly to your face, and greatly reduce leaking around the edges.

Weaknesses of Certified Masks

1. They are expensive, and eventually soil. They should never be washed, but can be re-worn a number of times.

2. Not all certified masks fit tightly to all face shapes - you might need to try different makes and models. And if you have a beard, none are likely to make a tight fit.

Cloth masks

Cloth masks are just what you think they are - the double and triple layers of cloth with elastic bands. You can make them yourself, or buy them for a few dollars, and they can be tossed in with your laundry after they are worn.

Some recent opinion columnists have loudly complained against using cloth masks as a tool to fight against Covid, to which I would respectfully, but firmly, disagree. Cloth masks are indeed imperfect, but for many families, they are only device that is affordable or available, and they still provide some benefit. The CDC agrees.

Cloth masks do a great job capturing large droplets as they exit your mouth, but have a few problems. They leak around the edges, and they aren’t the best for capturing the smallest droplets. The fabrics are porous, and let some of the small droplets leak through the mask. They also usually make a poor fit around your face, leaving wide gaps for droplets to pass through. Big giant droplets can’t make it through these gaps, but little droplets can.

Cloth masks remain popular, and I still wear them. But, knowing they have weaknesses, I take a more cautious approach when I find myself in a higher risk situation - in a crowded lecture hall, among large groups of people (indoors or outdoors), or with people who are not vaccinated. In these situations, it is wise to choose more protective face coverings such as certified masks.

Strengths of Cloth Masks

1. Inexpensive and can be worn many times after laundering.

2. Blocks most large particles that are exhaled from a wearer.

Weaknesses of Cloth Masks

1. The smallest droplets likely pass through most cloth materials. Both in and out.

2. Cloth masks can have a poor fit around your face, and can easily leak.

Surgical/Procedure masks

Surgical or procedure masks are inexpensive pleated masks with earloops. They are often light blue in color (but not always) and are sometimes, but incorrectly, called ‘paper masks’. You can usually find this type of mask being offered at the entrance to some public buildings, or given by local businesses who wish for their customers to wear a mask if they don’t have one. The fabric is better than cloth and does a better job capturing those tiny droplets, but can still leak around the edges. They often come with metal bendable strips designed to shape to your nose, which slightly reduces these leaks, though it’s still not enough.

In a way, surgical masks fall somewhere in between cloth and certified masks in terms of their effectiveness. The tightly-bound fibers in a surgical mask capture more of the droplets than the more porous fibers of a cloth mask. But that’s only if there is a tight seal, and surgical masks usually have a poor fit on your face. But here’s where we can use a trick to improve these masks: combine them with a cloth mask.

When you apply a poorly fitting surgical mask, and then a cloth mask on top, this seals up make of the leaks of the underlying surgical mask. It’s not a perfect solution, but in combination, it improves the performance of both masks, because the cloth mask presses the surgical mask closer to your mouth and nose, sealing up many of the gaps. When you take a breath (in or out), it is first forced through the surgical mask fibers, which capture most of those droplets. It’s simple and effective solution.

Strengths of Surgical Masks

1. Surgical masks are inexpensive and widely available.

2. The fabric blocks most droplets and across most sizes, but only if there are no leaks.

Weaknesses of Surgical Masks

1. Surgical masks almost always leak around the sides, and allow droplets to reach you. This may also allow some droplets to escape from the wearer.

2. They should be worn only once and then discarded.

Beware of Fraudulent Masks

One of the more worrisome aspects of certified masks are the presence of fraudulent masks available to consumers. The Centers for Disease Control (CDC), who certifies N95 masks in the United States, estimates that around 60% of all masks listed for sale as ‘KN95’ masks are fraudulent, and may not work well or at all. Many of these fakes are sold by national major vendors.

In my laboratory, we have tested some of these fake masks - they are simply no good. You may as well wear a tissue on your face.

A number of online sites, like Project N95, the Mask Nerd, and even the CDC provide useful guidance, though I’ll admit some of it is a little too technical for many to understand. When in doubt, stick with major US manufacturers, and beware of foreign distributors, especially those that are selling KN95 masks. And even major retailers like Amazon unknowingly sell many fraudulent masks, but most of these are through its vendor retail program and not Amazon itself.

And lastly, be careful of look-alike ‘certifications’. There is no such thing as a M95c or K95 standards (these standards don’t exist and are made-up marketing), nor are any KN95 masks marketed as ‘FDA listed’ (the FDA does not certify these masks and ‘listed’ has no meaning). These are likely to be low-quality masks that look and feel like better masks, but can be made with inferior or untested materials and are of poor quality. If you are unsure about a mask certification, a simple online search can be really helpful to weed out the junk.

Recommendations

First, choose a mask that you are willing to wear. Even the highest quality masks are totally ineffective if the mask isn’t worn.

Second, evaluate your risk. This includes assessing the conditions where you might need to wear a mask. Are there lots of people around? Is there a high community transmission rate? Are they vaccinated? Is there good ventilation? Do you (or your family members) have an increased risk because of preexisting medical conditions?

If the risks are high, wear the best mask that is available to you. Just make sure it fits tightly to your face. My choice is always a certified mask. If you don’t have access to these masks, layer a pleated surgical mask underneath a cloth one - this isn’t as good as a certified mask, but are better than a surgical mask or cloth mask by itself.

When risk is significantly lower, cloth masks should continue to be used. This doesn’t mean that certified masks aren’t needed - they still work extremely well, and if you are comfortable using them, then please continue to do so.

We all want the pandemic to end. So mask up and be safe. It’s the only way forward.