Last month, the CDC recommended double masking as one of several options to improve how your mask fits your face. If you’re one of many people who are now double masking, a new research letter recently published in JAMA Internal Medicine includes helpful insights into how to double mask more effectively.
A quick and valuable study by University of North Carolina researchers looked at the effectiveness of single and double-masked medical vs. cloth masks. Out of 4 brands of medical procedural masks tested and 3 kinds of cloth face coverings (1 brand of cloth mask, a cotton bandana and a polyester gaiter), they found that most procedural masks performed better than cloth face coverings. Doubling procedure masks modestly improved their performance. Doubling cloth masks improved performance but reduced breathability – not recommended. Most interestingly, wearing a procedure mask over a cloth mask was no better than wearing a procedure mask alone, but wearing a procedure mask under a cloth mask, as in the photo above, markedly increased mask effectiveness, for most double masking combinations.
You may be asking why a procedure mask is more effective inside than outside a cloth mask. The first thing to understand is that single-use procedure masks are generally one-size-fits-all but most of us don’t have one-size-fits-all faces. These masks were generally designed for average-weight, cleanshaven men but don’t fit women, children and bearded men’s faces as well. A lot of people find that procedural masks gap around the ears, leaving an open channel for air (and viruses) to leak out or in.
The CDC has recommended several options to address issues with incorrectly-fitting procedure masks: wearing a cloth mask over a procedure mask can hold the mask more snugly to the face. (In contrast, wearing an ill-fitting procedure mask over a cloth mask doesn’t add much value.) Knotting ear loops and tucking in the edges of procedure masks can also improve the fit. Mask fitters or braces can also help hold a mask more securely to the face, particularly for people with beards.
For those of us who wear cloth masks outside of medical settings, keep in mind that not all cloth masks are the same. Just as the recent UNC study found variations in the effectiveness of procedure masks, there are variations in the effectiveness and fit of cloth masks. Another JAMA Internal Medicine study published in December 2020 found marked variety in the performance of 7 cloth masks, ranging from 26.5% effective to 79% effective at filtering out small particles. Not all cloth masks are the same! In general, cloth masks with multiple layers of fabric (or with filter insets) and/or with adjustable nose wires tend to fit and perform better than plain one-size-fits-all single-layer masks. Although the CDC doesn’t comment on it, I also recommend getting face masks with adjustable ear loops so you can fit them to your unique face.
One thing to keep in mind before you double mask: don’t double layer N-95 or KN-95 masks over each other nor layer another mask over an N-95 or KN-95 mask. These masks are already 95% effective; adding another layer won’t significantly increase mask effectiveness but may reduce breathability. If you have an N-95 or KN-95 mask, wear it alone.
Stay healthy, get your shots and keep on masking,
😷 Dr. B