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Two Masks are Better Than One

Wearing a cloth mask over a procedural mask not only adds another layer, but helps flatten the edges of the procedural mask against the face, closing gaps.

This article was first published in The Montreal Gazette.

Over the course of this pandemic, recommendations regarding masks have evolved considerably. In the early days, when masks were in short supply, the recommendations were to use anything available as a face covering. Over time, recommendations evolved to include, first, two-layered masks, then three-layered masks, and now double masking.

You might be tempted to think that these ever-shifting recommendations represent either incompetence or capriciousness on the part of the people who write guidelines. But there is a method to the madness, and the current recommendations are based on our ever-growing understanding of how to control this pandemic.

It is hard to remember, but nearly a year ago when COVID-19 first entered our lexicon, things were in considerable disarray. Masks, among other things, were in short supply. Initial recommendations were to wear any type of face covering, and many people started to make their own. Eventually, recommendations evolved to recommend two-layer masks, then two-layer masks with an extra layer filtered in between and, with the supply shortage largely resolved, a general evolution toward wearing medical procedural masks.

It was largely believed that procedural masks were superior to cloth masks because they are made according to a certain standard, whereas the quality of cloth masks can be variable. Indeed, research early on suggested procedural masks would, on the whole, be the preferable choice. But new research by the U.S. Centers for Disease Control research suggests otherwise and finds that both procedural masks and cloth ones have room for improvement.

Masks depend both on the nature of their fabric and the fit. The thicker the fabric, the tighter the weave, and the more layers a mask has, the more effectively it will block the virus. But fit matters, too. Gaps between the mask and your face allow air to pass around the mask and limit its effectiveness. Wearing the mask with your nose sticking out effectively defeats the purpose.

One issue with procedural masks is that they can leave gaps on the side where air can leak out. As well, if you ever had your glasses fog up while wearing a mask, then that means air was leaking out the top and condensing on your lenses. To address this issue, researchers tested two strategies for improving mask fit in a series of simulation studies. One involved knotting the end of the procedural mask and tucking in the edges. The other option, which has garnered more attention, is to wear a cloth mask above the procedural mask. The goal is not so much to provide extra layering, though that probably does help, but to flatten the edges of the procedural mask against your face. Individually, cloth and procedural masks blocked just over half of the aerosolized particles in a simulated cough but combined they blocked over 85 percent. For its part, the knotted procedural mask blocked 77 percent. What’s more, when both individuals in this simulated interaction were double-masked, the cumulative efficacy rose to over 95 percent. Importantly, wearing two procedural masks doesn’t seem to provide the same benefit, as it doesn’t resolve the issue of gaps on the sides.

Double masking or knotting and tucking in the sides of a procedural mask seem to improve the efficacy of masks to limit the spread of COVID-19. For low-risk situations when you are outdoors and can keep a two-metre distance from someone, the extra degree of protection may be unnecessary. But in higher-risk situations, with the increasing number of potentially more infectious variants, the general feeling seems to be that optimizing mask-wearing has some benefits.

Some people may find double masking uncomfortable, but masks do not limit the flow of oxygen to your lungs and they pose no real harm. They are burdensome but necessary and with some simple tweaks, it appears that we can significantly increase their efficacy.


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