Masks do work, but mask policies are another thing entirely.

The use of masks to prevent the spread of Covid-19 has been controversial almost since the beginning of the pandemic, two years ago.

The U.S. Surgeon General made a huge early blunder, in February of 2020, when he recommended against masks, tweeting that

“masks are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!”

That self-contradictory tweet was later deleted, but it caused a tremendous amount of confusion. After all, if masks don’t work, then why is it so important that healthcare workers have them?

Masks do work. The evidence is overwhelming that masks, if properly worn, “substantially reduce exhaled respiratory droplets and aerosols from infected wearers and reduce exposure of uninfected wearers to these particles,” as described in a CDC publication last year.

The idea that masks should help prevent infections is intuitively obvious: Covid-19 spreads through the transmission of viral particles from an infected person. These particles travel through the air, as numerous studies have shown, just like many other infectious diseases. If you can stop the spread of the viral particles themselves, then (obviously) you stop the virus from infecting people.

However, evidence emerged early on in the pandemic that cloth masks and standard surgical masks were not very effective, because they allowed viral particles to leak out (and in). The SARS-CoV-2 virus is really tiny, and it can slip through the gaps in these masks.

In other words, some masks work better than others.

In June of 2020, a large study published in The Lancet reported that N95 masks were far superior at preventing transmission of Covid-19. That study found that “face mask use could result in a large reduction in risk of infection, with stronger associations with N95 or similar respirators compared with disposable surgical masks.” They reported an overall risk reduction of 85%, with N95 masks conferring a 96% reduction but surgical masks just 67%.

It’s easy to find studies showing how to make masks even more effective: make sure they fit very snugly, tightening them around the head or ears if necessary. Medical professionals who follow these guidelines have had very few infections, despite being exposed daily to sick patients. (Johns Hopkins Hospital, part of my own university, has reported almost no infections among its medical staff caused by exposure to patients.)

This all makes perfect sense. After all, if masks didn’t work, then doctors and nurses would have to be unbelievably self-sacrificing (even more than they are already) to treat Covid-19 patients. Fortunately, though, a properly worn N95 mask does an excellent job at protecting the wearer against infection.

One problem that often goes unmentioned, though, is that the better the mask, the harder it is to breathe. This too is pretty obvious: if you make it harder for tiny particles to get in or out, then of course it’s harder to breathe. Snug-fitting N95 masks are, simply put, uncomfortable.

Mask policies are the real problem. Even though masks work, getting millions of people to wear them, and wear them consistently and properly, is a far greater challenge. A casual stroll through any indoor space where masks are required–and we’ve all done this–will reveal many people whose masks don’t cover their noses, or whose masks are clearly very loose, or who might not be wearing masks at all, despite the rules.

Why don’t people wear their masks? This too shouldn’t be a mystery. Many people, young and old, simply don’t like being told what to do, so when a local government says they have to wear masks, they resent it. And governments (or large companies) have a habit of creating one-size-fits-all policies that are don’t make sense for some people. The simplest mask mandates (simplest to explain and enforce, that is) say that everyone should wear a mask all the time, or that everyone should wear a mask indoors.

For example, in Baltimore everyone has to wear a mask indoors, but restaurants are open. Thus diners must wear a mask from the entrance to their table, and then they can eat their dinner, mask-free, for as long as they wish. This doesn’t make much sense.

And what about people who are vaccinated and free from any Covid-19 symptoms? Nope, no exceptions, according to every mask mandate I’ve heard of. Naturally, that is frustrating to some people. No one should find this surprising.

In reaction to mask requirements, many people, particularly on the political right, have proclaimed that “masks don’t work.” While some of them might believe this–in which case they are just wrong–what they might really be talking about is masking policies, and in that sense they are right. If you can’t get nearly everyone to wear an N95 mask, then you can’t realistically control the spread of the virus.

We’ve seen how this works in the U.S.: despite widely varying mask policies, the Omicron variant has swept through every single state in the country, including those with strict mandates. Some places, like New York City, were hit earlier despite having fairly strict mask policies. States with no masking requirements and those that banned mask mandates (such as Florida, Georgia, South Carolina, and Tennessee), were hit later and just as hard.

One reason that masking policies don’t work–although masks themselves do work–is that it’s just really inconvenient to wear a mask all the time.

So people continue to wear masks badly, or to refuse to wear them at all. Does this mean we should give up? No, not exactly. But we might have to limit strict masking rules to places where truly vulnerable people are present, such as hospitals and senior care homes. Large-scale mask mandates are just not working, and there’s probably little we can do to change that in a free society.

A far, far more effective way to control the virus is through vaccination. As Eric Topol pointed out recently with an elegant graphic: “How to reduce your chance of dying from Covid by 99%? Get vaccinated and a booster.”

A new study out of Denmark tried to measure the benefits of masks. It didn't go so well.

Social media has been abuzz this week over a new study out of Denmark about the effectiveness of masks on the risk of getting Covid-19. Depending on what news source you looked at, you might have heard that masks might not protect the people wearing them, or that wearing masks doesn’t prevent the spread of the virus. You might also have read the near-immediate backlash in which scientists pointed out all the evidence that masks really do work.

I read the study. It doesn’t prove anything, as even its own authors admit.

Let’s dig into the actual results just a bit to see what all the fuss is about.

The study was conducted in Denmark in April and May of this year, and what it tried to do (not very effectively) was to measure the effect of a recommendation to wear masks. That’s right, they weren’t really measuring the benefits of masks directly at all!

The study enrolled about 6000 volunteers, and for half of them they recommended wearing masks whenever they went outdoors. They also provided masks to those volunteers. For the other half, they didn’t do anything. At the time (March and April), Denmark was recommending social distancing, but universal mask wearing wasn’t recommended.

Quite a few people dropped out, so in the end they only had 4862 people in the two groups, about 2400 per group.

What did they measure? Well, they did an antibody test (far from perfect, but let’s not digress) at the beginning of June to see whether or not people were infected with SARS-CoV-2, the virus that causes Covid-19.

(Note that they DID NOT measure how well the masks might have protected anyone else in the community. They were only measuring whether a mask might protect the wearer.)

And the results? 42 people in the mask-recommendation group were infected, and 51 people in the no-recommendation group were infected. (That’s 1.8% versus 2.1% of each group.) So there was a small reduction, but it was not statistically significant, which means we really can’t say if the mask recommendation helped prevent infection.

The study authors admitted this themselves, writing: “the findings are inconclusive ... compatible with a 46% decrease to a 23% increase in infection.” In other words, the results could mean that masks reduce self-infections by 46% or increase them (bizarre as that sounds) by 23%.

In other words, this experiment doesn’t tell us much. If it weren’t about Covid-19, I doubt that the Annals of Internal Medicine would have published it. (A commentary by my colleagues at Hopkins and Stanford suggested that Annals was right to publish it, as long as scientists “carefully highlight the questions that the trial does and does not answer.”)

Now some big caveats. First, in the mask recommendation group, only 46% of the participants wore masks as recommended. Second, the study didn’t ask if anyone in the no-recommendation group wore masks. Third, the study relied on self-reporting to determine who was actually wearing their masks consistently–that is, they simply asked the participants to tell them how often they wore their masks.

What? Imagine if you were studying the use of seat belts to reduce injuries, and only 46% of the people you told to wear seat belts wore them properly. On top of that, imagine that you relied entirely on self-reporting to determine who was actually wearing the seat belts. This study design is nearly worthless if you want to know the true benefits of seat belts.

So the Danish mask study was inconclusive, as its own authors report. Therefore it would be a huge mistake, scientifically speaking, to take this non-result and conclude that masks do not protect you. It would be an even bigger mistake to conclude that the study showed that masks don’t benefit the community. Unfortunately, that didn’t stop these two Oxford University scientists from jumping to exactly that conclusion. They claimed, in an article in The Spectator, that the study showed that “wearing masks in the community does not significantly reduce the rates of infection.” This is dead wrong. The study wasn’t even measuring community rates of infection.

(For an excellent Twitter-take on what the study does not prove, see this thread from The Health Nerd.)

And as the CDC has documented, multiple studies have already shown that masks are highly effective at limiting the spread of Covid-19. And a study last summer pointed out that increasing the use of masks by just 15% “could prevent the need for lockdowns and reduce associated losses of up to $1 trillion” in the U.S. alone. So yes, it’s a good idea to wear a mask.

It’s also simply common sense that if you wear a mask, the amount of virus that you breathe in or out will be reduced. You’re not just protecting yourself, you’re also protecting everyone around you.

Until we can get this pandemic under control, we all need to wear masks in public. It’s utterly ridiculous that this has become a political issue, as it has in the U.S. To those who think mask wearing somehow limits their personal freedom: get over it. When you see a red light at a busy intersection, do you race through it because you need the “freedom” to drive like a crazy person? No. Civilized society requires everyone to follow some basic rules to protect each other, and during a pandemic, wearing a mask is one of them. And to those who think that wearing a mask somehow shows their civic virtue? No, that’s wrong too. To use the same example, stopping at a red light doesn’t prove that you’re virtuous.

It’s just a mask. It’s not a political statement. Get over it.