Like many people, I’ve spent some times lately learning a few things about masks. I wanted to share some of what I learned, because I think it will be helpful. However, I’m doing this with some trepidation because…I’m not entirely sure this is the right thing to do.
That’s because, to be very clear, I am not an expert in this field.
What I am is curious about the technology involved, and I’ve therefore spent a bit of time trying to learn the basics of how masks protect us. My wife refers to me as a “PPE Enthusiast,” and I think that’s a pretty accurate characterization of my level of knowledge. And if I was talking about cameras or programming languages or something like that, I wouldn’t hesitate to give you my opinion.
But this is a matter of life and death, so I feel some caution is warranted, and I’ve seriously considered not posting anything at all for fear giving out bad information. But the thing is…I think I know some stuff that might actually help people.
So, now that I’ve fulfilled my duty of explaining my level of knowledge (not a lot, but more than some) and warning you that I might not know what I’m talking about, even though I think I do, let me see if I can offer you some advice about masks, starting with some basics about how we spread Covid-19.
Note about terminology: COVID-19 is a respiratory disease that is caused by a new strain of coronavirus called SARS-CoV-2. To keep things simple, I’ll just be calling everything “Covid-19” or just “Covid” here.
Most of the public health discussion about masks for Covid-19 is about what’s usually referred to as source control — preventing infections from spreading by stopping them at the source. For a respiratory infection, that means covering the breathing holes in your face with some kind of filter that catches the germs when you cough, sneeze, sing, talk, or even just exhale.
Germs are really tiny things — a human hair is about 500-700 times thicker than a single Covid-19 virus particle — but fortunately exhaled virions don’t usually travel alone. They’re usually stuck in all kinds of gooey fluids, and the resulting droplets of goop can be rather large, often large enough to see with the naked eye, especially when lit correctly, as in this photo of a sneeze:
That mess is what a source control mask is all about. If those droplets contained the Covid-19 virus, and someone inhaled one of them, there’s a pretty good chance they’d become infected.
Fortunately, it doesn’t take much to stop those big droplets. In everyday pre-pandemic life, people would cover their mouths with a handkerchief or paper towel when they sneezed or coughed. (And you may remember that very early in the pandemic they were advising people to sneeze into the crook of their elbow, just to absorb some of the mess.) What that implies is that you can achieve some measure of source control for Covid-19 with even a low quality mask, because it’s the equivalent of having a handkerchief positioned over your mouth and nose at all times, ready to catch any droplets you might exhale.
(It’s relatively easy to prove in a lab that masks will block exhaled particulates from talking or coughing. But studying the effectiveness of community masking — determining if mask wearing by large groups of ordinary people will actually prevent the spread of respiratory diseases — is harder. Prior to Covid-19, the studies were few and the results were mixed. But now that everyone in the world is part of a natural experiment, a whole bunch of studies seem to offer good evidence that masks are effective.)
If this were some other disease, we might just wear masks when we were sick, but with Covid-19, we unfortunately can never know when we might exhale droplets containing the Covid-19 virus…
One of the shocking early lessons of the Covid-19 pandemic was that people can spread the disease even if they’re not sneezing and coughing or, in fact, showing any other symptoms. Unlike many other respiratory diseases, the ordinary exhaled breath of someone showing no symptoms can still carry enough virus particles to infect someone nearby. Consequently, you can catch Covid-19 and then spread it to other people before you know you have it.
There was a somewhat confusing announcement from some World Health Organization scientists claiming that “asymptomatic” people did not spread Covid-19. Those scientists were using a highly technical definition of asymptomatic that refers only to infected people who never show any symptoms through the entire course of the disease, and even then it wasn’t entirely clear. But someone who shows any Covid-like symptoms, even symptoms so minor they don’t go to the doctor — or even realize it’s a symptom — could have infected other people before the first symptom occurred.
So just because you have no symptoms doesn’t mean that you aren’t infected. You could have it and not know it, and because you can infect other people with Covid-19 before you even know you have it, health authorities are recommending that we all wear masks at all times when we’re around other people.
That makes it sound simple, but I think it’s fair to say that there’s a non-trivial psychological burden: We have to behave at all times as if we are infected with a serious and potentially fatal disease. It takes a bit of getting used to.
The sneezing man above illustrates how someone with Covid-19 can literally spread it through the air. As you can see in the picture, however, many of the largest droplets are already falling toward the floor, and most of the rest will settle out of the air within a few seconds. Now a sneeze like that can carry pretty far in a few seconds, but the droplets that come out of your nose and mouth when talking or breathing normally aren’t moving nearly as fast, so they don’t get very far before settling out. This is the intuition behind one of the reasons social distancing works, even without masks.
(The 6-ft rule, I should add, is just a rough guideline. Coming to within 3 feet, or even 1 foot, of a person with Covid doesn’t guarantee you’ll get it, and being 15 feet away doesn’t guarantee your safety. But further away is always better.)
One important complication is that not everything that floats in air is going to settle out. The three major gases that make up the Earth’s atmosphere — nitrogen, oxygen, and argon — have different densities, but they have not settled out in billions of years.
Somewhere in between droplets (which settle out in seconds) and gases (which never settle out) lies a middle ground made up of…
Aerosols are particles or droplets that are so tiny they don’t fall out of the air — they are continuously buffeted about by the natural movements of the air. Familiar examples are fog, the fine smoke from a cigarette, or the lingering smell after cooking a meal. These can stay in the air for many minutes, until they disperse or stick to something.
In the early days of the pandemic, it was thought that under normal conditions, Covid-19 was only exhaled in droplet form, so aerosolized spread was not much of a risk outside of hospital settings (where certain procedures could aerosolize Covid-19 droplets). This was one of the reasons mask wearing was not encouraged in the early days of the epidemic — it’s not necessary if you’re keeping outside of droplet range.
Unfortunately, there has been mounting evidence for months, as the CDC has recently acknowledged, that people are exhaling Covid-19 particles in aerosolized form in quantities large enough to spread the disease. It is still not thought to be the most likely mechanism of Covid-19 spread, but since so many of us are mitigating against droplet spread by washing our hands, keeping our distance, and wearing cloth masks, aerosolized spread has become relatively more important.
Speaking of “relatively”…
The Numbers Game
Short of total isolation from the rest of humanity, you can’t make yourself perfectly safe from Covid-19. But you can control your level of risk, including the risk of aerosolized exposure. It’s a numbers game.
First of all, at least one viral particle — a virion — has to make it into your body and find a suitable host cell to successfully infect. No Covid-19 virions, no Covid-19 disease. Your body has some general-purpose defenses against viral infection, so the virion has to get a bit lucky to find a suitable cell to infect. Furthermore, scientists believe it generally takes more than one virion to cause the disease. I don’t understand why, and I’m not sure virologists have figured it out either, but in general, the more viral particles that make it into your body, the more likely you are to become infected, and (maybe) the more severe the disease is likely to be.
This means that the measures you take to mitigate the virus do not have to be perfect. Even a moderate amount of protection will improve your chances of avoiding infection, and if you get infected it might improve your chances of having a mild case. That is especially true when you pile on a bunch of different protective measures to reduce the risk of infection: They form a gauntlet that Covid-19 has to get through to get to you.
Here are some of the things you can control to reduce your risk:
- You can only catch Covid-19 from people who have it, so
- avoid people who seem likely to have it, and
- the fewer people you meet, the less likely you are to meet someone who has it, so avoid people in general and large groups of people in particular.
- Infected people breath out Covid-19, so the less they breath, the less Covid-19 you will be exposed to. Avoid people who are exercising, yelling, or singing. Silent people sitting quietly are your safest company.
- Even aerosolized Covid-19 disperses with distance, so the farther away you are from people who might be infected, the lower the level or your exposure. Distancing still helps.
- Speaking of distancing, the worst case of not distancing is getting Covid-19 virions on your hands and then touching your face. Wash your hands often, especially after touching other people or things other people have touched.
- Air flow disperses the virus as well, so outdoors is better than indoors, and good indoor ventilation is better than a stuffy room. (On the other hand, the wrong type of ventilation can just blow Covid-19 all over the room — imagine a Covid carrier sneezing in front of a fan.)
- When other people wear masks, they are less likely to spread Covid virions, so avoid people who are not wearing masks.
- Not only does your mask protect others, but it might help you as well, which is what the rest of this series of posts is all about.
None of these steps will make you completely safe, but you can, by combining these and other safety measures, make yourself considerably safer from Covid-19. Masks are part of that.
Next: Part 2: Types of Masks