The Centers for Disease Control and Prevention announced findings last week that suggest wearing two masks enhances your protection against the coronavirus by creating a tighter seal around your nose and mouth.
Yet some medical experts have long maintained that the chief benefit to wearing two masks is the increased filtration rather than the tighter fit, that two masks provide extra layers to capture any infected droplets you might exhale or inhale.
So, cleveland.com and The Plain Dealer contacted both medical experts and mask designers for the latest thinking on the question of one mask or two. Here is what we found:
Has the thinking changed over time?
During the early days of the pandemic, medical experts worried about infected droplets that are spewed when talking, coughing or sneezing and can be captured by single masks.
The experts scientists now understand that people also can become infected with COVID-19 through aerosols that linger in the air and can pass between slight gaps in ill-fitting masks.
New research, including that done by the CDC, also suggests that two masks can approach the protection provided by top-of-the line N-95 respirator masks that are used by health-care workers but are expensive and more difficult to breathe through.
How so?
The outer mask better seals the inner mask to our face.
And that snugger fit greatly improves performance by forcing air through the fabric, where coronavirus-laden particles and aerosols can be filtered out, and not around the edges of the mask, said Dr. John Brooks, chief medical officer for the CDC’s COVID-19 emergency response.
If there are gaps around the edges, air being inhaled and exhaled will take the path of least resistance, Brooks said.
Does it matter which two masks you wear?
Dr. Monica Gandhi, professor of medicine at the University of California at San Francisco, and Linsey Marr, professor of civil and environmental engineering at Virginia Tech University, recently released a report that discussed the potential benefits of wearing a thin cloth mask over a surgical mask made of polypropylene.
The cloth mask over the surgical mask has the benefit of forcing down the edges of the surgical mask to keep the air from escaping around the edges, Gandhi said.
This combination also provides better filtration.
The filtration efficiency of the surgical mask is enhanced by an electrostatic charge created by the polypropylene that helps capture the droplets, Gandhi said. In an interview with NPR, Colorado School of Public Health epidemiologist May Chu described the effect as being like static cling.
A second option the two doctors highlighted was a “three-layer mask with outer layers consisting of a flexible, tightly woven fabric that can conform well to the face and a middle layer consisting of a non-woven high-efficiency filter material (e.g., vacuum bag material).”
How was the CDC research done?
The report by Gandhi and Marr prompted the CDC to test the double-mask scenario using mannequins and simulated breathing experiments in a lab, Brooks said.
The CDC also tested a system of knotting and tucking the loops on a medical-procedure mask to see if simply having a snugger fit with a single mask improved filtration.
One of the experiments found that when a mannequin functioning as the “receiver” of the virus wore a cloth mask over a medical procedure mask, and the mannequin expelling the virus had no covering at all, the “cumulative exposure” to the receiver was reduced by 83 percent. The efficiency dropped to 64.5 percent when the receiver wore only a medical procedure mask that had its ear loops knotted near the edges for a tighter fit and the extra material tucked and flattened against the face.
The results were slightly less effective when the source of the virus was coming from the double-masked mannequin and the receiver was not masked.
When both the wearer and the source were wearing the two masking options the level of protection exceeded 95 percent.
But Brooks cautions against reading too much into the performance values assigned to the experiments because they were conducted in a lab with specific kinds of masks. In the open market, there is a great deal of variation in masks.
Ranu Dhillon, an instructor at Harvard Medical School, considers the double mask scenario to be better than many other options. But he would still opt for wearing an N-95 type mask because it gives you around 95 percent protection even when you are around people who are not wearing a mask.
What do mask makers say?
Justin Bloyd would agree with Dhillon. Bloyd’s company, RB Medical Supply in Mentor, makes N-95 and high-quality surgical masks.
“I think the double mask is good advice so people have more protection,” he said.
But he questions why somebody would wear two masks when they can wear a single N-95, dismissing some health experts who have said the N-95s are difficult to properly fit , are more expensive and are more difficult to breathe through.
Bloyd believes the CDC is not willing to recommend that the public wear N-95s because it would prompt a run on the masks and possibly create a shortage for the frontline workers who rely on them.
A spokesman for 3M, which makes all manner of masks, released a statement in the wake of the CDC’s report that addressed the trend toward wearing two masks and concerns about doing so.
“Double masking may work for certain styles and models of face coverings and people should consult the face covering user instructions and CDC guidance for direction,” according to the 3M statement. ” . . . . A face covering, or double face covering combination, should only be worn if comfortable enough to keep on the whole time you are in public settings or near people outside of your household. Combinations of face coverings that are very difficult to breathe through may not be suitable to be worn for long periods of time or may result in increased leakage around the edges. “
3M spokesman Tim Post said the company’s reusable cloth face mask, developed a couple months ago, is not designed to be worn in combination with another mask and that its primary function is to reduce the volume of droplets that someone expels from their nose and mouth.
