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The US Centers for Disease Control and Prevention issued new guidance last week that urges Americans to wear the highest quality mask they can wear consistently and that fits well. Specifically, they classify the masks by level of protection.

“Loosely woven cloth products provide the least protection, layered finely woven products offer more protection, well-fitting disposable surgical masks and KN95s offer even more protection, and well-fitting (National Institute for Occupational Health and Safety)-approved respirators (including N95s) offer the highest level of protection,” the CDC recommendations read.

Many public health experts have been urging this change for months, including CNN Medical Analyst Dr. Leana Wen. I spoke with Wen to answer some common questions about masks.

Wen is an emergency physician and professor of health policy and management at the George Washington University Milken Institute School of Public Health. She is also author of “Lifelines: A Doctor’s Journey in the Fight for Public Health.”

CNN: Why have you been urging the CDC to make this change in mask guidance?

Dr. Leana Wen: We’ve known for over a year that Covid-19 is airborne. Quality of mask matters when trying to prevent an airborne infection that’s so highly transmissible. This is particularly important now that we have the extremely contagious Omicron variant. We should be empowering people to wear the right mask — the best mask — that protects them.

CNN: What mask would you recommend people wear?

Wen: In indoor, crowded settings, I highly recommend that people wear an N95, KN95 or KF94 mask. The N95 is the American standard; KN95 is the Chinese standard; KF94 is the Korean standard. They can all be highly effective in terms of how well they protect against Covid-19 transmission.

The CDC emphasizes consistency, which are both very important. Some individuals will find these respiratory masks to be uncomfortable. I suggest that they try out different kinds of masks. Someone might find an N95 to be too constricting, but a KN95 to be fine. Others prefer the feel of a KF94. There are some that have elastic loops on the ears versus over the head, and different people have a preference there, too.

An N95 respirator that's fitted well and worn consistently is a highly effective way to protect against Covid-19 spread, CNN Medical Analyst Dr. Leana Wen said.

CNN: What if someone doesn’t find any of these masks comfortable?

Wen: If someone really can’t consistently wear a respiratory mask, they should double-mask. Consider wearing a medical-grade surgical mask, then put a well-fitting, finely woven cloth mask on top.

CNN: How does someone know if what they’re purchasing is real versus counterfeit?

Wen: Buy masks from trusted sources. Project N95 is a national nonprofit that has links. Purchasing from the supplier directly — for example, 3M or Kimberly Clark — can also help reduce risk. CNN’s Dr. Sanjay Gupta has additional tips on how to spot counterfeit masks.

The Biden administration is also making 400 million non-surgical N95 masks available to Americans for free starting next week. The masks should be made available at a number of local pharmacies and community health centers by early February.

In related news, the federal government has also launched a website to send people free Covid-19 tests. People can order a maximum of four tests, which will be shipped to their homes.

CNN: Should I look for an N95 with a valve or without one?

Wen: I would advise that you look for N95s that do not have an exhalation valve. The ones with valves protect the wearer very well, but it’s possible that if you are infected, virus particles could escape from the valve and infect others. The level of virus escape is pretty low, though; according to the CDC, N95s with an exhalation valve work about as well as surgical masks or cloth masks in terms of protecting others. So, if an N95 with a valve is the only one you can tolerate wearing, you should wear that, but it’s not recommended above an N95 without a valve. And make sure to try KN95 or KF94s – these might be even more comfortable for you.

CNN: These respirator masks are expensive. Do they need to be thrown out every day?

Wen: No, they can be reused. How many times they are reused depends on their condition and how often they’re used. Someone who is using masks every once in a while to go to the grocery store might be able to reuse the same mask for weeks. Someone else who’s using it the entire day for work might have to change them out every few days.

Use common sense when deciding whether it’s time to replace the mask. Throw it out if it’s clearly dented and out of shape or if it’s wet or soiled – for example, if you sneezed in it.

CNN: Do they need to be cleaned?

Wen: No, and I do not recommend that you try to clean them. Spraying with sanitizer or water, or microwaving the mask, could damage the mask beyond repair.

Some people are worried about the mask carrying virus on it. There’s little evidence of surface transmission of Covid-19, but if you want to be extra safe, have two or three masks that you are using in rotation every day. When you are done with one mask for the day, put it into a plastic bag or container. Use another one the next day, then come back to the first mask. Remember that if it’s soiled or damp, throw it out and use a new one.

CNN: What about kids — can they also wear respirator masks?

Wen: There are some KFN94s and KN95s available for children, but it’s worth reminding people that fit is really important. Some children find them to be comfortable. If not, a surgical mask with a cloth mask on top would be a good alternative.

CNN: There’s a lot of uncertainty about what’s going on with the Omicron variant and Covid-19 more generally. Is there at least certainty about the importance of masking?

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Wen: Yes, masking is an important layer of protection – especially when there is this much virus circulating. Know that even if others around you aren’t consistently wearing masks, you can wear a high-quality mask that still protects you. I really want everyone to be upgrading our masks to the best mask that we can consistently wear, and wear them in indoor, crowded places.

This story has been updated with additional information about N95s with exhalation valves.