Is one-way masking enough?

Face masks work best to prevent the spread of SARS-CoV-2 when everyone wears one. But experts say it is still worth wearing a mask to protect yourself, even if no one else does.

While public health messaging has tended to emphasize the importance of wearing a mask to protect others, numerous studies have demonstrated that the right mask protects the wearer, too.

“We have collectively done a poor job at communicating the strong efficacy of N95 respirators,” according to Lisa Brosseau, a bioaerosol scientist and industrial hygienist at the University of Minnesota’s Center for Infectious Disease Research and Policy.

Recent data from the United States shows that people who always wore a face mask in indoor public settings were less likely to test positive for SARS-CoV-2 than those who never wore a mask.

Better quality masks offered greater protection. Wearing an N95 or KN95 respirator lowered the odds of infection by 83%, whereas wearing a surgical mask or cloth mask lowered the odds by 66% and 56%, respectively.

Fit matters, too. Properly fitted N95 respirators should filter at least 95% of virus particles. That’s notably better than the protection offered by universal masking with cloth and surgical masks, which would have fallen on the lower end of 75%–91% at the height of compliance with mandates.

Even a loose-fitting N95 can filter 57%–86% of particles, according to Japanese research. In comparison, surgical masks filtered 47%–50% of particles, while a simple cotton mask filtered 17%–20%.

However, the protection masks offer is time-limited.

In 2021, Brosseau and colleagues estimated it would take up to 1.25 hours for a person wearing a non-fit-tested N95 to receive an “infectious dose” of SARS-CoV-2 from an unmasked infectious person. In contrast, it may take just 15 minutes if both people are unmasked, or 20–30 minutes if one of them wore a cloth or surgical mask.

Brosseau has since cautioned that these estimates don’t account for highly infectious variants like Omicron and should not be taken as a “bright line between when you’re safe and when you’re not safe.”

The findings of a more recent modelling study suggested that a person has a 90% risk of infection within a few minutes of speaking to someone with SARS-CoV-2 if neither is wearing a mask, even if they’re standing three meters apart. Wearing the European equivalent of an N95 mask dropped that risk to 20%, even after one hour.

“Just wearing a mask — it helps, but it is not going to turn being indoors into something that has no risk,” Jose-Luis Jimenez, an aerosols scientist at the University of Colorado Boulder, told NPR. When it comes to crowded indoor environments with poor ventilation, “I don’t think it can be made very safe,” he said.