One of the common arguments I’ve read against wearing a face mask to protect against SARS-CoV-2, is that doing so means I will be breathing in my own Carbon Dioxide.
I don’t understand what the problem is with this though. I think it’s true that if I’m wearing a face mask, I will be breathing in Carbon Dioxide that I’ve just exhaled from my lungs. Then again, it’s also probably true of when I’m not wearing a mask, since every inhalation of breath, tends to immediately follow the last exhalation of breath, and it’s probable that I will be inhaling some of what I just exhaled. I think some of the people making the argument about inhaling my own Carbon Dioxide, pre-empt this possible counter argument, by adapting their argument to suggest I will be breathing in *all* of the Carbon Dioxide I just breathed out, if I’m wearing a face mask.
My first challenge here is straight forward, which is that Carbon Dioxide is so tiny, it’ll mostly have penetrated the mask, by the time I inhale again.
My second challenge, is essentially, so what?
I have checked the science here, from various sources, all of which suggest that breathing in Carbon Dioxide, is normal.
The approximate most significant percentages of what is contained in a single inhalation of air are Nitrogen (78%), Oxygen (21%).
Those alone account for about 99% of the volume of a single inhalation of air. Then the remaining 1% consists of small amounts of things like Argon, Hydrogen, Helium, and of course, Carbon Dioxide.
The percentage of volume for a single inhalation of air, for Carbon Dioxide, is about 0.04%.
This is for inhaling when not wearing a mask though. Combine this with my first point, then maybe it’s still possible that I’ll be significantly increasing the volume of Carbon Dioxide I will be breathing in, by wearing a mask?
Just 0.04% of the air we breathe in, is Carbon Dioxide, however, the amount we breathe out, is 100 times the amount we breathe in!
The amount of Carbon Dioxide in a single exhalation of air from our lungs, is normally about 4%.
The approximate amounts we breathe out are as follows (these won’t add up to 100%):
- 5.0–6.3% water vapor
- 79% nitrogen
- 13.6–16.0% oxygen
- 4.0–5.3% carbon dioxide
- 1% argon
Then we’re into Parts Per Million and trace amounts of things.
Breathing out 100 times the amount of Carbon Dioxide than we breathe in, sounds pretty bad, but it’s still only 4%. Then, if we assume that a percentage of that 4%, escapes the mask we’re wearing, it’ll be even less.
For the sake of the argument, let’s assume that we do breathe back in, all 4% of the Carbon Dioxide we just breathed out. Although I’ve realised this also doesn’t make sense because if we’re only ever breathing out what we just breathed in, plus our bodies using and converting some of the good stuff, then we’re going to suffocate. Perhaps this is part of the argument for not wearing a mask, however, if Carbon Dioxide can get out through the mask, it can also get in through the mask, and if Carbon Dioxide can, it’s likely Oxygen can too. Plus the fact that some people wear masks all the time without ever suffocating to death. Maybe I should have just written that to begin with and the argument is over, but where’s the fun in that.
So I’m going with the idea that while wearing a mask, I will be breathing back in, 100% of the Carbon Dioxide I just breathed out (4% of the volume of my last breath).
Let’s bung in something else for fun, and say I will also be breathing in Carbon Dioxide that I didn’t breathe in from my last breath, so, assuming the mask doesn’t filter out Carbon Dioxide (or not to any significant amount), then that’s 0.04% of my inhalation of air.
I may be hitting some serious statistical nonsense here, as I’m starting to lose the will to live just thinking about this, no idea how other (non scientists or mathematicians) have managed to reach their conclusions!
If I’m breathing in the air from immediately around me, including inside my mask, then for this argument, I think I’d be breathing in about 4.04% Carbon Dioxide while wearing a mask, rather than 0.04%. Maybe?
Since we can’t have more than 100% of a breath, I guess that means if we’ve got an increase in volume intake of Carbon Dioxide, wearing a mask, then that has to take the space of something else. Most of what we breath in (and out) is Nitrogen (around 79%). I don’t know if Carbon Dioxide discriminates in what other gas it takes the place of but assuming it’s being fair, then it’s going to distribute relatively evenly across all the other contents of the air we’re breathing.
So I think I need to lose 4.04% across everything else?
Let’s see, something like, Nitrogen (76%), Oxygen (19%), Carbon Dioxide (4.04%), and since the rest is in tiny amounts, it’s probably not worth bothering with.
Since we don’t appear to be too bothered about Nitrogen as we breathe in roughly the same amount as we breathe, it leaves Oxygen, which has lost 2% to Carbon Dioxide. Oh no!
Well, it’s only 2% but surely we need all the Oxygen we can get out of a breath?!
Apparently not, since we normally, without a mask, breathe in 21% Oxygen, then breathe out up to around 16%. Which suggests we are using only 5% of the 21% or Oxygen in the air we breathe in.
If I’ve done this right, then my conclusion here, is that the very unsafe assumption, that we’d be breathing back in, all of the Carbon Dioxide we previously breathed out, probably has absolutely no impact on the quality of the air we’re breathing in as a result of wearing a mask.
The only other thing I can think of at this point, is that wearing a mask restricts breathing. It doesn’t necessarily significantly change the ratio of the gases in the air, but in effect, makes it more difficult to do the action of breathing. So one possible detrimental effect might be that the muscles we use, and possibly our lungs, have to work harder, and that could create strain, but only potentially use up more Oxygen for doing the breathing, but we know that we take in more Oxygen than we use, so we have that overhead. Additionally, I have a theory that many people, are efficient at breathing, sounds weird maybe, but I’m not sure myself, what the best way to breathe is. Is it to take slow deep breaths, or quicker, shorter breaths? Where I am going with this is that maybe wearing a mask could force us to be more aware of our breathing, and for example, breathe more slowly and deeply. If breathing more slowly and deeply, is better for us (I guess this depends on what we’re doing), then perhaps wearing a mask is beneficial in that way?
The final, but possibly most important thought, around the possible detrimental effects of wearing a mask, is the emotional impact. Perhaps the main issue isn’t any physical impedance of breathing, it’s the possibility of fear that our breathing is being restricted, leading to poor breathing regulation, or even panic.
I haven’t written about it in this post, but I do believe there is a benefit of wearing a face mask, in terms of reducing risk of the spread of SARS-CoV-2. Weighing that up against the risks of wearing one, suggests to me that the risks in terms of wearing a mask, are very small, apart from the psychological impact, which I can mitigate by being aware of my breathing, and so it makes more sense to wear a face mask (in public, especially an enclosed space) than not wear one.