Question: I’m legit skeptical about wearing two masks.  Why do it?  

Answer: The point of double masking is to improve the filtration of viral particles, and the main mechanism of improved filtration is improved mask fit.  As it turns out, a cotton mask over a surgical mask can dramatically improve mask fit, thereby reducing the amount of viral particles expelled into / inhaled from the surrounding air.  We last talked about double masking in our Q&A of 2/1.  Since then, CDC has updated its guidance on improving mask fit (Figure  1) and just last week, JAMA published a new piece of research on the subject, Fitted Filtration Efficiency of Double Masking During the COVID-19 Pandemic.  Study researchers found that wearing a medical procedure mask [e.g. surgical mask or disposable mask] underneath a cloth mask provided the best improvement to filtration efficiency of all the combinations evaluated.  Looking at other combinations, they found that: a) double masking with two cotton masks improved filtration efficacy, but reduced breathability; and b) putting a medical procedure mask over a cotton mask or over another medical procedure mask only modestly improved filtration efficacy, likely because it only modestly improved mask fit.  Ultimately, there’s some nuance with wearing two masks– the benefit of some combinations is not all that additive– but the benefits are meaningfully important when it comes to the combination of a medical procedure mask topped by a cloth mask that pushes the edges of the disposable mask against your face.  Since SARS-CoV-2 is an airborne virus, the better we are at masking, the better we are at protecting others and ourselves.   

Figure 1. Improving Mask Fit (from CDC)