How to know when you should double-mask, when one mask is enough, and which masks you should use

CDC/Bing Guan/Reuters
  • Wearing a cloth mask over a surgical one can greatly reduce coronavirus transmission.
  • Knotting and tucking a surgical mask so that it fits better is very effective, too.
  • Other mask types can be paired given the situation, but no amount of masking will be enough to completely let down your guard.
  • Visit Business Insider’s homepage for more stories.

When it comes to preventing the spread of COVID-19, we know that more distance between people is better than less, smaller crowds are safer than larger, and outdoor activities are less risky than indoor ones.

We also know that a wide variety of face masks work to protect both the wearer and those around them. So are two better than one? Dr. Anthony Fauci has hypothesised that the answer is yes, as have experts on virus transmission.

And now, there’s evidence they’re right. According to a study out of the Centres for Disease Control and Prevention February 10, if everyone double-masked, we could reduce COVID-19 exposure by 96.4%, Insider’s Hilary Brueck reported.

But that doesn’t mean wearing two masks is right for everyone, since a well-fitting one can be nearly as effective. Here’s how to figure out what works best for you.

Should I should wear two masks, and why?

In general, face masks work by blocking the large respiratory droplets that spread the virus when people sneeze,or cough. They can also serve as a barrier against smaller aerosols, a less common but still possible way the virus transmits.

The CDC study showed that while a single surgical mask on an infected person blocks about 42% of infectious particles from reaching a healthy person and a cloth mask blocks more than 44%, wearing a cloth mask over a surgical one blocked 92.5% of cough particles.

Cdc double masking improves fitCentres for Disease Control and PreventionThe CDC tested single masks, double masks (surgical + cloth on top), and knotted and tucked masks.

When both parties (or dummies, in the case of the study) are double-masking in this way, the protection 96.4%, Brueck reported. That seems to be because the surgical mask filters out virus particles well, while the cloth mask can improve the fit.

Stephen Morse, a professor of epidemiology at the Columbia University Medical Centre, told Insider he’s found this strategy is more comfortable than a single mask, as it helps prevent the inner lining from sticking to his face when he breathes.

When is one mask enough?

If two masks is irritating to you, don’t force it. “The real limit is likely to be comfort. Can you breathe through the combo?” Morse asked. “Otherwise, you might not fit it closely enough to your face, and then it could be less protection than one good, well-fitting mask.”

A well-fitting mask should seal around the nose and mouth, preventing droplets from escaping through any gaps.

Cdc double masking improves fitCentres for Disease Control and PreventionThe CDC tested single masks, double masks (surgical + cloth on top), and knotted and tucked masks.

The CDC study found you can make a single surgical mask fit better by knotting the ends and tucking the fabric so it better hugs the face. That strategy, it found, is almost as effective as double-masking.

One mask may be sufficient in certain situations, too. Biking solo through a sparse neighbourhood, for instance, requires less protection than standing in a crowded grocery store line.

If I’m going to wear two masks, which types should I pair?

Wearing a cloth mask over a surgical one is a proven strategy to reduce coronavirus transmission, but other pairings likely work well too. For instance, Fauci has demonstrated wearing two cloth masks, saying it makes it “more firm and comfortable.”

Doubling up this way may offer extra protection if, for example, you’re using two single-layer cotton masks, ideally with a high thread count (around 600). That way you can mimic a mask that has two layers, which research has shown is superior to a single-layered cloth mask.

Healthcare workers in short supply of N95s, meanwhile, may benefit from wearing a surgical mask on top in order to keep them cleaner and help them last longer, Morse said. Fauci has also done this at some early press briefings, Morse noted.

North dakota coronavirusBing Guan/Reutersegistered nurse Dana Simmers’ glasses fog up as she dons a 3M N95 protective mask before beginning her shift at a drive-thru testing site inside the Bismarck Event Centre, North Dakota.

Dr. Deborah Birx, the White House coronavirus response coordinator, has also recommended wearing a shield over a cloth mask.

You can also mimic a so-called “hybrid” mask by combining two layers of 600-thread-count cotton mask paired with another material like silk, chiffon, or flannel — an April study found such masks filtered at least 94% of small particles and at least 96% of larger particles, Business Insider’s Aria Bendix and Yuqing Liu previously reported.

That aligns with the World Health Organisation’s recommendation that fabric masks have three layers: an inner layer that absorbs, a middle layer that filters, and an outer layer made from a nonabsorbent material like polyester.

Coronavirus face mask portrait  25Crystal Cox/Insider

Wearing multiple masks is not so protective that you can let your guard down

Doubling up may do more harm than good if they give you a false sense of security, leading you for example to spend more time with strangers indoors or slip up on social distancing.

“You cannot become overly reliant on any one measure,” WHO infectious disease specialist Maria Van Kerkhove said during an October media briefing. “It can’t just be testing alone, it can’t just be case identification alone, it can’t just be masks alone, it can’t just be physical distancing alone. All of these different interventions need to be used.”


Editor’s note: This story has been updated to include CDC guidance released February 10.

Business Insider Emails & Alerts

Site highlights each day to your inbox.

Follow Business Insider Australia on Facebook, Twitter, LinkedIn, and Instagram.