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Do masks really work? What does the science say?

Masking is a critical public health tool for preventing spread of COVID-19. To protect yourself and others from COVID-19, CDC continues to recommend that you wear the most protective mask you can that fits well, and that you will wear correctly and consistently.

Recommendations are not “mandates”, however.


Political polarization of masking

Masking is a very polarized topic because there are many people who are of the opinion that masks do not work, that mask mandates were simply a form of “government control”, and any suggestion of bringing back mitigations to protect public health during surges is responded to with conspiratorial social media posts suggesting “we are headed for a lockdown”. And who can forget the many videos of grown adults throwing tantrums at Wal-Mart greeters who were asking shoppers to don a mask during the height of the pandemic?


Cochrane Review

Adding fuel to the anti-mask fire was a highly misunderstood Cochrane review paper published in January of 2023. This meta-analysis review went viral on social medial with many people misrepresenting its purpose and conclusions. What the review actually examined was whether promoting/encouraging mask wearing helps to slow the spread of respiratory viruses, and the results were inconclusive.

The authors of the review noted many limitations to the available evidence, so the review was not actually able to answer the question of whether the masks themselves reduce the risk of respiratory viruses. Importantly, Cochrane reviews rank evidence from randomized clinical trials (RCTs) most highly in its algorithm. RCTs are great for assessing the efficacy for drugs or vaccines, but RCTs are not the best study design for assessing the efficacy of behavioral protective factors like masking. A clarification was published in March, 2023 on the Cochrane website by their Editor-in-Chief to clarify this widespread, gross misrepresentation of the results.


What the science says

Well-fitting masks are effective at reducing transmission of COVID-19 when worn consistently and correctly. Generally, masks should have a proper fit over your nose, mouth, and chin to prevent leaks, have multiple layers, and have a nose wire.

If masks are ill fitting, not worn at all, not worn correctly, or not worn by many people, this obviously effects their efficacy on both individual and population levels.


In February 2022, the CDC published a study that found that consistently wearing a well-fitting mask in public protects reduces the risk of COVID-19 between 56-83% depending on the quality of the mask worn. The study found that any mask is better than no mask, but that cloth masks have the lowest efficacy. This study was the rationale for recommending higher quality masks (N95/KN95) to combat the more infectious Omicron variant. A large community-based masking study also replicated this finding that cloth masks had lower efficacy during the Omicron period.



Additionally, we have a lot of data that shows that masks work best if everyone wears one. These data on the efficacy of universal masking informed the scientific rationale for public masks mandates during the most active parts of the pandemic.


The bottom line:

During an outbreak, the best mask efficacy is when well-fitting, high-quality masks are universally worn, the worst mask efficacy is when no masks are worn, and there is a lot of gray area in effectiveness between those two extremes (for example, other protection measures like vaccines, social distancing, and ventilation interact with masking to decrease disease risk).


So, the answer to the question “do masks work?” is yes, they definitely work when a high-quality, well-fitting mask is worn correctly and consistently. But in a community setting, it is more difficult to nail the exact efficacy down due to so many people having different masking and general disease prevention behaviors.


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