This study does not explain why masks lower the severity of COVID-19

The Quarantine Zone
1

To stop the hijack of the Breaking News thread, if anyone wants to make the claim that this study proves anything about the method by which masks help reduce severity or why one mask type is better than the other due to the results, this is a good place.

Study in question.

I’ll start with the lead author’s own statements about the study:

We found that face masks strongly increase the humidity in inhaled air and propose that the resulting hydration of the respiratory tract could be responsible for the documented finding that links lower COVID-19 disease severity to wearing a mask

High levels of humidity have been shown to mitigate severity of the flu, and it may be applicable to severity of COVID-19 through a similar mechanism

“Could”, “may”, and “propose” don’t even reach the level of “likely” or “probably”. The only thing definitive in those statements are that masks reduce severity of influenza and that masks increase humidity in inhaled air, neither of which I disagree with.

In regards to which mask is more effective than others, I’ll note: the below picture is of one of the authors demonstrating the method of measurement. You’ll notice that the edges of the mask are outside of the chamber, a chamber which is lined with high density foam to reduce leakage. This removes from the equation the fact that some masks have a better seal around the edge than others and could therefore impact humidity levels inside of the mask.

What the research actually attempted to study was the level of humidity inside various mask types. It did not look at which masks are most effective against inhalation or transmission of the COVID-19 virus. Even the NIH, who was behind the study, recommends going to the CDC for guidance when choosing a mask. Due to the issue of leakage removal as noted above, I’m not even sure that the humidity results (the only thing the study actually measured) are valid.

With all of that said, I happen to like the fact that another researcher says wear a mask, even if they don’t prove the reason that it is so effective. Just don’t take the results here and start extrapolating from them regarding effectiveness of different mask types against COVID, nor that humidity levels definitely have any effect on COVID.

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As an aside, I can find nothing that demonstrates that this has been peer reviewed. Anyone have evidence to the contrary?

3

Since I seem to have (inadvertently) caused a kerfuffle that led to this thread, I should comment.

As a scientist, I was concerned that the terse description that this was a letter, not an article (whatever that is…) would leave many readers of the thread that somehow this was like a letter one would find in the opinion pages of a newspaper. I wanted to make sure that anyone reading the thread got better context on the worth of the cite.

That said, after I submitted my post I went back and skimmed the paper and noted to myself that it did not make any significant claims, just provided interesting data and discussions about potential underlying reasons, with some quantitative analysis of what looked like reasonably constructed experiments with known limitations.

In other words, a pretty solid bit of science worthy of publication in a peer reviewed journal.

And that was it. I don’t believe my comment took sides, but it did provide context for someone deciding whether it was worth reading.

4

You have to dig into the menu in the upper right to look through the publications information. The description of editorial practices describes a peer review and the fact that it has an impact factor and is traced in Scopus is an indication of the quality of the peer review, as is the publisher.

I’ve run the gamut in my career- author, peer reviewer, editor, editor-in-chief, and oversight of a society’s publications, so I have an unfair advantage in recognizing peer reviewed journals in the wild.

5

I have heard speculation from medical peeps that the viral load you get hit with has some impact on if/how sick you get. A mask isn’t perfect, but it reduces the aerosolized droplets, especially if everyone is wearing them. If all parties wear masks properly and keep social distancing yadda yadda, it seems to effect severity.

6

I claim that ordinary surgical facemasks, worn in the way I ordinarily wear them, substantially reduce the amount of water I lose by breathing in a dry environment.

I make this claim based on years of data. Back when SARS-1 was in the news, I bought a case of 150 surgical masks, thinking that if SARS wasn’t contained, masks might become hard to buy. Then they sat in my closet for a while. Then, one day, I had to fly somewhere, but I had a mild cold. So I decided to wear a facemask to protect my seatmates from my cold.

It was the most comfortable flight I’d had in years. I realized that a lot of the symptoms I thought were due to “jetlag” were actually due to my becoming dehydrated in the extremely dry air of airplanes.

I’ve worn a facemask on long flights ever since. For most of that time, I made a point of explaining to my seatmates why I was wearing the mask, so they wouldn’t think I had tuberculosis or something scary. I don’t mind if strangers think I’m a dork, but I didn’t want to scare random people.

I used to drink lots of water on airplanes, to avoid dehydration. And it just went through me. I had to pee frequently on long flights, and my eyes/nose/throat nonetheless dried out. Once I started wearing masks, I found that I didn’t have to drink extra water, and ALSO my eyes, nose, and throat remained comfortably moist. (Why eyes? I suppose just because they share moisture with the nose.)

Yes, this is an N of 1. But the difference is striking and completely repeatable.

So I’m going to say that it doesn’t matter that the mask fits loosely around the edges. Surgical masks enormously reduce the amount of water I lose by breathing.

(I mean, probably they wouldn’t when the humidity is high. But airplanes have super dried air.)

I haven’t explicitly tested how well cloth masks hold in moisture. But I’ll take the author’s word that they hold in moisture even better.

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Also, here’s the key hypothesis of the study:

Here, we propose that the increased humidity of air inspired through face masks is responsible for the lower disease severity of mask wearers. In contrast to the primary function of masks of preventing virus from entering the respiratory tract of another person, this additional benefit applies after a virus-containing particle lands on the surface of the respiratory tract; reduced dehydration limits impairment of the innate immune system while improving mucociliary clearance , with both these factors reducing infection probability. If an infection does occur, humidification may limit its further spread through the lungs by lowering the generation of virus-containing breath droplets that could lead to self-inoculation elsewhere in the lungs . At the same time, effective mucociliary clearance and an unimpaired innate immune system of the well-humidified respiratory tract also may limit viral spreading, allowing more time for mobilization of the adaptive immune system. The effect of humidity on respiratory viral disease is increasingly recognized, as exemplified by the recent proposal to use elevated humidity as a nonpharmaceutical intervention for influenza A

FWIW, I have been using a humidifier in my bedroom to protect against covid, because I’ve been convinced by previous studies that low humidity decreases the immune efficiency of the respiratory track.

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Same here. It wasn’t a comment on the paper itself. I felt compelled to explain that letters, research communications, etc. are peer reviewed. The only difference is that they tend to be shorter pieces of work with less data, etc. I just couldn’t help myself!

I agree that all they tested was humidity in the mask. I’ve read a lot of papers speculating that mask humidity increases the size of droplets entering the mask preventing them from being inhaled too far down the respiratory tract. I thought that’s what the authors were going to discuss, but their hypothesis is that it would help moisten the respiratory tract and improve the innate immune system. I assume that can be tested too. Anyway, I thought it was a cool idea.

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Yes, it’s very interesting and the paper allows other scientists to build on it, either helping confirm or refute the hypothesis.

For the non-scientists reading the thread who are wondering what the big deal about peer reviewed literature is, the simplest way I can put it is:

A peer reviewed paper is not guaranteed to be right, but it is very, very likely to be true.

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Exactly!

11

This was really my point. They tested humidity level increases based on mask type and I’m not convinced they did so accurately, due to the method they were using and the shortcoming that could be seen in the picture. As noted above, I love when studies tell people that masks are useful, even if I don’t agree with the method that they used to arrive at that conclusion. There are plenty of other studies telling them that they aren’t.

Additionally, I do think the potential effect of humidity on this virus is interesting, but that study did nothing that I could see other than introduce it as a talking point. The current reality is that there is a metric shit-ton of research around COVID, much of it shoddy or given more validity than warranted. We have studies that say don’t wear a mask. We have studies that say smoking reduces the COVID risk. There was a peer reviewed study that claimed that 5G could lead to a coronavirus infection. Pretty much every paper that used the Surgisphere data is crap. The problem has gotten so out of hand that MIT Press is actually attempting to address it. The other side of that coin is that some of that rush could be seen on the vaccine research side, which has had a positive impact.

In the end, the Breaking News thread is a bad place to have this sort of conversation, so I created this thread.