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Banner image:听Students, staff and baby直播app, on the first day of the 2020 Fall semester on the CU Boulder Campus. (Credit: Glenn Asakawa/CU Boulder)

As several new variants of the novel coronavirus are now circulating the U.S., many people are wondering: Should we be wearing two face coverings instead of one?听

The idea of double masking was recently touted on the TODAY show by Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), and on Feb. 10, the to address wearing two masks听based on the .听

CU Boulder Today spoke with our own Jose-Luis Jimenez, chemistry professor and , about this new trend and why in fighting the COVID-19 pandemic.听 (Learn more about why wearing a mask is important, even outside, and where you can pick up your free CU Boulder reusable face covering on campus.)听

How do masks protect us from the virus that causes COVID-19?听

Masks work when the air that we inhale and exhale goes through the mask material. Then a lot of the aerosols that may contain the virus stick to the material, which protects the wearer from breathing them and others from the aerosols exhaled by the wearer.

What are the two most important elements of wearing a mask, single or double?听

What matters for masks are two things:听

One, the quality of the material鈥攈ow many of the aerosols that go through the material stick to it. Single layer cloth masks have low filtration, while three-layer cloth masks or two layers with a filter in between, or surgical and N95 masks have good filtration.

Second, the fit of the mask to the face. If there are gaps between the mask and the face, most often on the sides of the nose or the sides of the face, then a lot of the air we inhale or exhale will move through these gaps鈥攊nstead of through the filter material. If the gaps are 2% of the surface area of the mask, 50% of the air we breathe will go through there without any filtering.听

What are the pros and cons of different types of masks?听

Cloth masks vary widely, but larger cloth masks can actually fit better than N95 in many situations. N95 masks are not easy to fit, and hospitals routinely do fit testing to teach people how to do it well. Surgical masks tend to have gaps on the sides, although this can be improved enormously with cheap devices such as .听

Should we all be double masking?

I don't think double masking should be our default. I would advocate for a high-quality mask with attention to fit, and to make sure that you don't have gaps and don't develop gaps. Men should shave any beard on the areas where the masks sits, as it is impossible to get a good seal there鈥攁 lot of the air goes through the hair and is not filtered.

What is the best way to double mask, and when does it make sense to do so?听

For double masking, we have to think in terms of filtration and fit. In some cases, it makes sense to double mask, for example: In hospitals they wear a surgical mask on top of an N95, which can keep the N95 clean if someone was to cough on it. Another potentially useful method is to wear a larger cloth mask on top of a surgical mask, so that the cloth mask helps close the gaps of the surgical mask.听

Can double masking be done improperly?听

Double masking can create problems. For example, depending how the second mask sits on top of the first one, it may increase the gaps of the first mask, leading to less filtration. In addition, because the air a person is breathing in and out encounters more resistance by having to go through two masks, a larger fraction of the air may go through any gaps present, defeating the purpose of the masks.听

Is there any harm in wearing a mask or two masks?听

To my knowledge there is no harm in wearing a mask. Sometimes people say that the mask retains carbon dioxide and that can cause oxygen depletion. But the amount of air between your mask and your face is very small compared to how much air we breathe, so your body compensates by breathing slightly faster, and the oxygen saturation does not change. Anyone can do this experiment with a pulse oximeter and a couple of scientific articles have demonstrated it.听
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Wearing a mask is something we鈥檝e had to adjust to and it makes communication more difficult. But it is a change that we have to live with for the time being to avoid the much larger problems of getting COVID-19, and of potentially passing it on to others who may die from it or suffer long-term health consequences.听