Masks seem like they couldn’t possibly work. How could wearing a little piece of cloth possibly be effective?

Evidence: Masks Work

However, there have been a lot of real world studies that masks do actually work at reducing infections. They are not perfect, but they do significantly lower the risk of the wearer and the people around the wearer. Here are some studies:

  • This HUGE study in Bangladesh sent people out to villages to stand around and remind people to wear masks. The reminder-people had zero enforcement authority, all they did was remind people to mask up. The compliance, even with reminders, still wasn’t great (42% in those villages, vs. 13% in non-reminder villages), but there was a statistically significant difference in how many cases and deaths villages had depending on whether they had reminder-people or not.
  • This study found that schools without mask mandates were 3.5 times more likely to have outbreaks than schools that had mask mandates.
  • This study found that children’s case rates were 2.1x higher in counties without mask mandates than with.
  • This page from the US CDC lists a ton of studies.
  • This review article (from Jan 2021) cites a lot of studies.
  • This paper reports that 66% of hamsters in a cage adjacent to a cage with COVID-infected hamsters got infected themselves. (There was one infected hamsters in one cage and three uninfected hamsters in the other cage. Two exposed hamsters were examined after five days, and the other at seven days.) When a barrier of surgical mask-material was placed in between the pair of cages, only 12.5% of the exposed hamsters got sick when the fabric was placed to simulate the sick hamster “wearing a mask”, and 37.5% of the exposed hamsters got sick when the fabric placement simulated the exposed hamsters “wearing a mask”; the “masked” hamsters also got less sick than the “unmasked” hamsters in the first part of the study.
  • This article reports on a study looked at the difference between counties in Missouri which had mask mandates and those which did not, and found that the risk of COVID-19 was 37% higher in counties which did not have mask mandates.. (See graph below.)

How Masks Work

But how can masks possibly work? Breath goes

  • Masks don’t have to stop all the virus to help. The more virus particles you are exposed to, the sicker you get. Thus, if a mask keeps a lot of the particles from going out / coming in, even if it is not all, that’s a win.
  • Masks catch a lot of the particles in your breath. How many? I don’t know, and it will vary depending on the mask. However, catching some is better than none, because the more virus particles you inhale, the sicker you get.
  • Humidity helps. There are a number of papers I have read that say that respiratory viruses are sensitive to humidity. One thing I’ve read is that when the air is drier, the droplets you expel evaporate faster, making them smaller, making it easier for them to surf on air currents and stay in the air. Another is that the respiratory tract doesn’t do as good a job of conveyor-ing out junk when it’s dry. Well, when you wear a mask, the humidity of what you inhale and exhale goes up. Maybe this makes your respiratory tract work better and you produce more droplets and fewer aerosols. (Note: this is my theory, I’ve never heard anyone else float this theory. I could be all wrong.)
  • Masks change the breath direction. When you talk to a friend without wearing a mask, your breath goes forwards, right towards whoever you are talking to. When you are wearing a mask, even if the air leaks out the sides, it is no longer going forwards: it’s going up or backwards, not towards your friend. (Watch this video of a woman exhaling smoke through various masks.)
  • Masks slow breath down. When your breath is redirected through the top or sides of a mask, it slows down. The slower breath particles go, the more they will fall to the ground.
  • Masks are more effective when the contagious people wear them. Masks work best when the droplets are big, and the droplets are biggest right when they come out of your mouth/nose.

I don’t know if lighter fluid is a good proxy for COVID-19 or not, but this video of someone shooting lighter fluid through a mask / no mask is entertaining, at least!

Scientific Modelling

Here are some papers which talk about measurements of aerosols or which do mathematically modelling of virus dispersion with and without masks:

  • This paper says that if two people are speaking, one infected and one not, at a distance of 1.5m:
    • If neither is wearing a mask, the susceptible person is 90% likely to get infected after just a few minutes.
    • If the infected person is wearing a surgical mask and the susceptible person is not wearing a mask, the susceptible person won’t hit the 90% likely threshold until 30 minutes.
    • If the infected person is wearing a FFP2 mask and the susceptible person is not wearing a mask, the susceptible person will only be 20% likely to be infected after until 60 minutes.
    • If both people are wearing surgical masks, the susceptible person will be under 30% likely to be infected after 60 minutes.
    • If both people are wearing FFP2 masks, the susceptible person will be under 0.4% likely to be infected after 60 minutes.
  • This paper says that not every exhaled particle has a virus in it, and that in most environments, there are few enough that a surgical mask can deflect enough that a surgical mask is usually good enough. (For hospitals, or arguing nose to nose with an anti-vaxxer, you ought to have an FFP2.)

Recommended Reading/Viewing

This video talks about masks.