Face masks comparison

There has emerged a rough rule of thumb for face masks that says that when it comes to reducing the chances of transmission of the covid-19 virus, N95 masks are the best, with paper surgical masks next, and cloth masks the least effective, compared to wearing no mask at all Now the CDC has come out with a study that provides a more quantitative comparison.

Here is how the study was done.

A test-negative design case-control study enrolled randomly selected California residents who had received a test result for SARS-CoV-2 during February 18-December 1, 2021. Face mask or respirator use was assessed among 652 case-participants (residents who had received positive test results for SARS-CoV-2) and 1,176 matched control-participants (residents who had received negative test results for SARS-CoV-2) who self-reported being in indoor public settings during the 2 weeks preceding testing and who reported no known contact with anyone with confirmed or suspected SARS-CoV-2 infection during this time. Always using a face mask or respirator in indoor public settings was associated with lower adjusted odds of a positive test result compared with never wearing a face mask or respirator in these settings (adjusted odds ratio [aOR] = 0.44; 95% CI = 0.24-0.82). Among 534 participants who specified the type of face covering they typically used, wearing N95/KN95 respirators (aOR = 0.17; 95% CI = 0.05-0.64) or surgical masks (aOR = 0.34; 95% CI = 0.13-0.90) was associated with significantly lower adjusted odds of a positive test result compared with not wearing any face mask or respirator. These findings reinforce that in addition to being up to date with recommended COVID-19 vaccinations, consistently wearing a face mask or respirator in indoor public settings reduces the risk of acquiring SARS-CoV-2 infection. Using a respirator offers the highest level of personal protection against acquiring infection, although it is most important to wear a mask or respirator that is comfortable and can be used consistently.

Wearing an N95/KN95 respirator (aOR = 0.17; 95% CI = 0.05-0.64) or wearing a surgical mask (aOR = 0.34; 95% CI = 0.13­-0.90) was associated with lower adjusted odds of a positive test result compared with not wearing a mask (Table 3). Wearing a cloth mask (aOR = 0.44; 95% CI = 0.17-1.17) was associated with lower adjusted odds of a positive test compared with never wearing a face covering but was not statistically significant.

I just received my quota of three free N95 masks issued by the government and distributed through pharmacies and I will be wearing them until the incidence of the virus becomes categorized as endemic.

This raises an interesting question as to whether we should adopt the practice in some countries, particularly in Asia, where people wear masks whenever they have any symptoms of a cold or other respiratory problem that is not serious enough to warrant staying at home. Somehow I think that the US does not have level of civic consciousness where people will do that, given that so many people refuse to wear masks even in the face of a raging pandemic.


  1. says

    By chance, I saw a paper saying further studies (not just the observational one from China in 2020) show that eye protection makes a difference. I might post about it tomorrow.

    Goggles work best, but wrap around eyewear that leaves no gaps also work well.

  2. Malcolm says

    I use a cloth mask but it has a pocket for a PN2.5 charcoal filter which is claimed to stop particles >2.5 micrometres. Not sure how this would fit in that list.

  3. xohjoh2n says


    The paper, if you search it, appears to specifically state that it doesn’t distinguish between any types of cloth mask and thus treats them all as bad as the lowest common denominator. Furthermore anyone involved who reports wearing more than one type of mask was treated as always wearing the worst type of mask reported.

    This is unfortunate, but a reasonable research choice if their population is limited.

    Other outlets (for example the pyramid chart on PZ’s recent post) seem to suggest that a cloth mask with a PM2.5 insert is equivalent to a surgical paper mask. I’m happy with that news because locally it has become almost impossible to source disposable surgical masks (the UK’s largest retail pharmacy has been out of stock for 3 months) so cloth+filter is the current mask type I’ve had to go for.

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