Q&A

COVID-19 and Face Masks: Your Questions Answered

Medical-grade masks provide better protection than cloth masks against the highly contagious Omicron variant. SPH professors in the Department of Environmental Health share guidance on how to select, wear, and preserve KF94, KN95, and N95 masks.

Jonathan Levy is chair and professor of environmental health; Wendy Heiger-Bernays is a clinical professor of environmental health; and Patricia Fabian is an associate professor of environmental health.

Why use masks to protect against COVID-19?

It is well established that COVID-19 is spread via airborne viral particles and the virus is transmissible from presymptomatic, asymptomatic, and symptomatic people to uninfected people. When people breathe and talk, the virus is expelled and small viral particles remain in the air for long periods of time until the air is diluted with “clean” air or the air is filtered. The most effective method for decreasing exposure to these viral particles is with masks, alongside adequate room ventilation and filtration. Masks decrease release of viral particles from infectious people and decrease inhalation of viral particles by other people in the room. The Omicron variant is even more infectious than previous variants, making it even more important to use masking and ventilation/filtration to reduce exposure. Several reliable studies have examined the effectiveness of different kinds of masks, with consideration of fit and comfort.

Why use KF94, KN95, or N95 masks?

These masks do much better at keeping you from inhaling the virus. A typical cloth mask removes up to maybe 50% of the airborne particles. The performance of surgical masks depends greatly on the degree of fit. If worn with no measures to reduce gaps, your protection may not be better than cloth masks. Performance can be increased to 60-80% filtration by knotting and tucking ear loops and otherwise minimizing gaps, and better still if using a mask brace, A well-fitted KF94/KN95/N95 can be more like 90-95+ percent. That’s actually 5-10 times better than a cloth mask—for every 100 particles in the air, 50 would be inhaled with 50 percent removal, but only 5 would be inhaled with 95 percent removal. As with many other respiratory viruses, it is likely that the more virus you inhale the more likely you are to get infected. And if everyone wears masks, the benefits are multiplicative, since the masks would filter out both what is being exhaled and what is being inhaled, resulting in smaller inhaled doses.

What is the difference between KF94, KN95, and N95 masks?

All these masks have similar filtration efficiency. The labels just have to do with what country provided approvals—KF94 is tested and approved by the Korean FDA. KN95 is the equivalent from China. N95 is approved by US NIOSH (National Institute for Occupational Safety and Health). Any of these three would be appropriate for use at BUSPH. N95s generally have straps that go behind your head rather than ear loops found in KF94s and KN95s, which both provides a tighter fit and greater long-term comfort, but you can find comfortable and protective KF94s or KN95s.

How do you decide which mask to purchase, given the importance of filtration efficiency, comfort, and fit?

Three things matter—filtration efficiency, comfort, and fit.

For filtration efficiency, if authentic and tested, all of these types of masks do well, but performance can vary. NIOSH does testing of N95s, but you can find systematic testing databases that include KF94s and KN95s elsewhere.

For comfort, along with the straps versus ear loops, you want to make sure the masks are breathable so you can wear them for multiple hours. One little-known fact is that the best KF94/KN95/N95s are actually more breathable than cloth, and more comfortable. You can teach in them and hike in them, wearing them comfortably for many hours.

Fit is key—you can have the best filtering mask material in the world, but if there are gaps where air can come in and out, you are breathing air that is not filtered. If you can feel your breath coming out of the sides or your glasses fog up, you do not have an adequate fit. Ideal fit can be challenging for some people, including those with facial hair.

However, it is incorrect that without a formal “fit test” you cannot have a protective mask. There are some very easy informal “fit tests” you can do at home. One is to simply blow out and see where you feel air, but following is a reasonably rigorous one that Rich Corsi (an expert on the topic) uses:

• Place several small mirrors or reading glasses (or knives or spoons if you don’t have mirrors or reading glasses) in the fridge for 2 to 3 min. Avoid putting them in the freezer, as they will get too cold and you will get condensation on lenses when you remove them.
• Take the first one out and place it directly in front of your mask. As you breathe, the high water vapor content of your warm breath will condense on the lens, a good thing as it shows air going through the mask.
• Now take out a second pair of glasses/mirrors/knives/spoons and put it at the edge of the mask near your chin, nose crease, or cheeks. You want to see as little, and preferably no, condensation as possible. Lack of visible condensation does not mean zero leakage, but does give a good indication of relative fit. Aim for zero visible condensation around edges and a lot adjacent to the front of the mask.
• It is best to do the front of the mask first and edges after, as glass lenses will become cooler as they sit in the fridge and yields a safety factor (makes it easier to get ample condensation even with small leakage).

Can I wear the KF94, KN95 or N95 more than once?

Yes, you can actually wear them multiple times without a problem. But do not wash them! Good practice is to have a few (label with numbers or days of the week!) and rotate them—wear one and hang it up or put it in a paper bag for a few days, then reuse. You can generally get about 40 hours of use out of a KF94 or KN95, as long as they don’t get wet or too disgusting. Also watch that the elastic doesn’t stretch out or the nose piece loosen, which will decrease the effectiveness because it will not fit as well. The N95s typically fail at the straps before they fail at the mask, so watch for strap stretching or breakage.

Can I be heard and understood while wearing more efficient masks?

For normal conversation, it is not a problem. Many of these masks have more space between the mask and your mouth than cloth masks, which leads to less muffling. For teaching, this will depend on the classroom and on the instructor, as well as on the mask itself, so it is important to practice teaching with the mask. Some BUSPH faculty are heard and understood and others require the use of a microphone.

Where can I purchase more efficient masks?

One warning is that there are a lot of counterfeits on the market, especially for KN95s sold on Amazon. So it is not recommended to buy these masks from Amazon. Projectn95.org is a reputable non-profit that has great options and regularly restocks. Some Korean vendors sell the authentic KF94s with lots of options—kollecteusa.com is one, but there are others.

Which specific masks people should get is a matter of personal preference, what fits your face best, and other logistics. A few models that score very well and have been described as quite comfortable by people are the Gerson N95 3230, Indiana foldable A105 N95, the Bluna FaceFit K94, or 3M Aura N95. But there are many others that could work well.

Also, these vendors generally sell in packages of 10-50, so it can be a big investment to find out something doesn’t fit well. One idea would be for some people to group together and order a few different types, and share them to see what works well for different people.

REMINDER: Per university guidance, all staff, faculty, and students are required to wear masks on campus. Starting Wednesday, January 19, the University will make available KN95 masks to all faculty, staff, and students. The masks will be distributed to faculty and staff through the on-campus COVID testing locations, and can be picked up at your next regularly-scheduled test. These masks can be safely worn for up to 40 hours or approximately one week as long as they are not visibly soiled and have not lost their shape. BU will make available 4 or 5 masks per person, which will enable use of a KN95 mask for the next month.