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What’s the Evidence on Face Masks? What You Heard Was Probably Wrong

Despite hearing that face masks “don’t work,” you probably haven’t seen any strong evidence to support that claim. That’s because it doesn’t exist.

Adrien Burch, Ph.D.
Mar 19 · 10 min read
Photo by author.

We can’t stay locked in our homes indefinitely. When the day comes to restart our normal lives, we should do everything possible to prevent the coronavirus from spreading uncontrolled through our communities. That is why we need to start a serious conversation about Covid-19 protection — now.

Early on, there were a lot of assurances from the media and various government organizations that face masks are ineffective and could potentially increase our risk of infection. So many assurances, in fact, that some airlines and other businesses won’t allow their employees to wear masks even while working in high-traffic, high-risk locations. This could prove to be a deadly mistake.

Despite hearing that face masks “don’t work,” you probably haven’t seen any strong evidence to support that claim. That’s because it doesn’t exist. Yes, the Covid-19 death projections are looking grim, but we can still beat this disease — if each of us is armed with the information we need to prevent ourselves from catching and spreading it. That’s why it’s about time for Americans to look at the data and reassess our opinions on face masks.

What Research Is Relevant?

Covid-19 is a brand-new disease, which means scientists are still scrambling to learn the basics, including how to best prevent its transmission. This lack of data is why we must look at other, closely related examples for guidance.

Although Covid-19 is a novel disease, it is caused by the SARS-CoV-2 virus, which is closely related to the virus that caused the SARS epidemic 17 years ago. However, since Covid-19’s true genetic identity was not widely publicized until recently, influenza research probably shaped doctors’ initial opinions about face masks instead. What does the actual science say about SARS?

According to research on the SARS epidemic, face masks were the most consistently effective intervention for reducing the contraction and spread of SARS. In a Cochrane Review on the subject, six out of seven studies showed that face masks (surgical and N95) offered significant protection against SARS. Hand washing was also very effective, supported by four out of seven studies in a multivariate analysis.

Although most of the studies in the Cochrane Review were on medical workers in a hospital setting, one study followed community transmission of SARS in Beijing. It found that consistently wearing a mask in public was associated with a 70% reduction in the risk of catching SARS. Additionally, the authors of the paper noted that most people in the community wore simple surgical masks, not N95 respirators.

This may be why public health agencies in many other countries encourage — or even require — the general public to wear face masks. It may also be why the CDC currently recommends that we wear face masks while in the same room as a sick family member who is not wearing a mask.

Of course, one of the most important takeaways from this data is that our hospital workers are in extreme danger given the current face mask shortage. Additionally, it is essential that we learn how to properly wear a mask, since another review on SARS health care workers emphasizes that face masks offer the most protection when they are used consistently and worn properly.

In general, influenza reviews are more in line with current advice about prioritizing hand washing. Whereas most influenza studies are consistent about handwashing being good, they are somewhat inconsistent about face masks being helpful. Most studies in the above-linked influenza review found face masks to be useful protection against influenza, although the following two studies had contrasting results.

One study showed that children who improperly used masks caught H1N1 2% more often than children who didn’t wear masks (not statistically significant, if you are wondering). However, since the children in the study who wore face masks correctly cut their risks in half, the researchers suggested they should all be taught proper mask technique. The other study found an increased risk associated with wearing face masks, but based its conclusions on only 14 cases of H1N1.

Another frequently referenced review on face masks and influenza states the familiar warning that masks could increase your risk of transmission. However, their cited evidence is not a research study, but a WHO info sheet about face masks that makes the same claim — without any citations to back up the claim.

If Covid-19 was floating in the air, free of fluid, it would be around 100 nanometers in size. N95 respirators can only filter out 95% of particles sized 100–300 nanometers. Surgical masks offer even less protection. So the answer is yes — viruses can technically pass through both types of face masks.

But will they? That is less certain. When a person coughs, the droplets are typically somewhere between 8,000–100,000 nanometers in diameter. Most of these droplets, especially the large ones, will quickly settle and end up on surfaces. The smaller droplets stay in the air longer — but are still large enough that a properly-fitted N95 mask could filter them out, since N95 masks are 99.5% effective against particles sized 750 nanometers or bigger.

Since most virus-containing fluid will end up on surfaces, it remains important to wash our hands regularly and avoid touching our faces when in public. One of the strongest arguments in favor of both surgical and N95 masks is that they help prevent us from touching our faces with dirty hands when used correctly.

Face masks might offer some protection from airborne viruses in droplets, especially if the droplets that carry them remain a large-enough size. But if you are in a dry climate and the liquid evaporates before the droplets can settle, Covid-19 might end up in a droplet that is too small to be filtered by a face mask. Also, researchers have warned that SARS could be aerosolized (made into a very tiny droplet) by nebulizer therapy and CPAP machines, which would help it penetrate face masks. This warning might be important for hospitals and nursing homes.

There is an ongoing scientific debate as to how much benefit comes from wearing N95 respirators instead of surgical masks. When used properly, N95 might offer more protection since it filters out smaller particles (discussed above) and also creates a tighter seal against the wearer’s face than a surgical mask. On the other hand, N95 masks are less comfortable, are frequently misused, and are taken off more often than a surgical mask.

Theoretically, N95 respirators might be a better choice if you are taking care of someone with Covid-19. When used properly in a medical setting, N95 respirators were more effective against SARS than surgical masks in three different studies.

However, when moved out of a hospital setting and into everyday life, those differences could even out. If we look at the data on influenza, reviews typically conclude that N95 respirators are not significantly more effective than surgical masks. This is likely why the public is being advised against wearing N95 masks.

Of course, stores are sold out of both surgical and N95 masks, which means that homemade masks are the only option remaining for many of us. Even hospitals are using and requesting homemade fabric masks — that’s how bad this shortage is. Although none of the above research applies to fabric masks, there is a little bit of research on this topic.

An important thing to keep in mind is that every cloth will have a different weave, which allows larger or smaller particles to pass through. As you might imagine, researchers find that N95 respirators are more effective than cloth at preventing small particles from passing through. However, fabric masks might be comparable to some surgical masks.

If you do wear a fabric mask, treat it as you would a disposable mask and don’t reuse it without ensuring it has been sterilized. Fabric mask disinfection is not an active research topic, but the standard wisdom of running it through a long, hot wash is supported by research showing that the SARS virus can be inactivated by high heat and detergent. UV light can also be used against SARS, but since the light needs to reach the virus in order to inactivate it, UV might not effectively sterilize porous fabric.

Most importantly, we don’t want our nation’s supply of face masks to be depleted while we’re still in the early stages of the pandemic and our risks are relatively low. Maintaining the health of our medical workers is essential at this stage.

While wearing a mask, you might end up touching your face more often and transferring the virus from your hands to your face. In order to avoid this, wash your hands both before and after adjusting or removing your face mask.

If your mask becomes moist against your skin, viruses could diffuse across the mask and reach your face. If you are a medical worker or taking care of someone who is sick, this is very important. However, since viruses are not alive and cannot replicate outside of a living cell, there is no risk that a face mask will somehow increase the quantity of viruses you are potentially exposed to. Any quantity of viruses that diffuse across a wet face mask will still be fewer compared to if you weren’t wearing a face mask.

Used face masks need to be sterilized or disposed of properly. Hospitals are currently figuring out ways to sterilize and reuse disposable face masks. If you are disinfecting multiple face masks, make sure that the wearers’ names are written on the masks and never used by anyone else. Ethylene oxide or heat treatment at 70C/160F for 30 minutes might be the best options for sterilizing porous face masks.

Should You Wear a Face Mask?

Like handwashing, face masks can only offer partial protection against Covid-19. The best defense right now is exactly what we’re being told to do by the experts — completely avoiding exposure to the SARS-CoV-2 virus through social distancing. So long as you’re staying home and nobody else in your home has been exposed to the virus, you should not wear a face mask.

However, some of us currently live with sick family members, and the rest of us will eventually need to come out of hiding. Based on the research, face masks are much more likely to help than to hurt. Even if it’s just a homemade cloth mask, if you wear it correctly and avoid touching it, the science suggests that it won’t hurt you and will most likely reduce your exposure to the virus.

The unfortunate reality is that our country does not currently have enough disposable face masks in reserve to keep our health care workers safe. Please don’t hoard face masks or take them from medical facilities — health workers will need them the most in the coming weeks. And if you currently have extra face masks or the skills required to craft homemade ones, you might consider offering them to hospitals and others who are exposed to the highest risk — like transportation and grocery store workers.

There are currently not enough disposable face masks for everyone, which means that our government cannot mandate us to wear them — even though doing so might be a smart move. The only way we could put masks on everyone today is if we start making our own out of fabric or other readily available materials. In theory, fabric masks could offer similar protection to surgical masks, but there has not been enough testing for official agencies to advise the public to do this.

Decreasing the demand for face masks was a valuable strategic choice at the beginning of this pandemic. But public demand no longer threatens the medical supply — since neither the public nor hospitals have access to new face masks. That is why it’s now time to switch gears and discuss the benefits of face masks instead of the negligible risks. Let’s talk about why it’s urgently necessary to put face masks on our medical workers, even if all we can offer them are our homemade masks. And then let’s talk about us.

Beyond self-protection, one of the most compelling reasons that we should all wear face protection in the upcoming months is to ensure that silent spreaders also cover their faces. People are predicting that this pandemic could last a very long time. Although our country does not currently have enough face masks for everyone, if we ramp up innovation and production now, we could be covered in the future.

Next Steps

Here are some resources for face mask construction and innovation. Please comment if you have any other resources to add.

Better Humans is a collection of the world's most trustworthy writing on human potential and self improvement by coaches, academics, and aggressive self-experimenters. Articles are based on deep personal experience, science, and research. No fluff, book reports, or listicles.

Adrien Burch, Ph.D.

Written by

Ph.D. in microbiology from University of California, Berkeley. B.S. in molecular biology from Yale University. Taught microbiology at UC Berkeley. @AdrienYBurch

Better Humans

Better Humans is a collection of the world's most trustworthy writing on human potential and self improvement by coaches, academics, and aggressive self-experimenters. Articles are based on deep personal experience, science, and research. No fluff, book reports, or listicles.

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