Many Americans are confused, some even outraged, about the Centers for Disease Control and Prevention’s new recommendations to return to mask-wearing. But while nearly half the U.S. population is vaccinated against the coronavirus, health officials are concerned about the rising numbers of new infections attributable to the highly transmissible delta variant – coupled with low vaccination rates in many areas of the country.

Furthermore, while the authorized coronavirus vaccines remain highly effective at preventing severe disease, hospitalizations and death from the delta variant, data suggests that fully vaccinated people with breakthrough infections – which are still considered rare – can spread the virus.

All of these factors mean masks remain an important tool in slowing the spread of the virus.

The CDC underscored that point by issuing a revised guidance on July 27 urging Americans, fully vaccinated or not, to mask up in public indoor spaces under certain circumstances.

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Below we’ve compiled answers to some of the most commonly asked questions surrounding masks and how to use them in this latest phase of pandemic life. These recommendations are drawn from CDC guidance, previously published Washington Post articles and new interviews with experts specializing in infectious diseases, public health and air quality.

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Please keep in mind that as the coronavirus, its variants and vaccines continue to be studied and understood, masking advice is likely to change.

– What is the CDC’s latest guidance on masks?

The CDC, which in May said it was generally safe for fully vaccinated individuals to go maskless in indoor public spaces, is now advising all people, regardless of vaccination status, to mask up in such places if they are in areas reporting “substantial” or “high” transmission of the virus. This will “maximize protection from the Delta variant and prevent possibly spreading it to others,” according to the CDC.

The CDC is also urging universal indoor mask-wearing in K-12 schools for everyone over the age of 2. Masks should be worn by teachers, other staff members, students and visitors, even if they are fully vaccinated, the CDC says. (The agency’s recommendation that students return to in-person learning in the fall has not changed.)

Fully vaccinated people might want to consider wearing a mask regardless of the level of community transmission, the guidance notes, particularly if they or someone else in their household is immunocompromised or otherwise at risk of severe covid-19 disease. People who are at increased risk include older adults and those with underlying health conditions, such as diabetes, obesity and heart problems, among others.

– How do I know whether I’m in an area with substantial or high transmission?

Substantial transmission is defined as 50 to 99 weekly cases per 100,000 people, while high transmission is defined as more than 100 weekly cases per 100,000, The Washington Post’s Amy Goldstein reported. As of Aug. 2, more than 78% of U.S. counties met that definition, according to the CDC’s tracker.

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You can monitor transmission rates in your community by using the CDC’s tracking tools and following guidance from local public health officials.

– Why did the CDC change its guidance?

The agency was prompted to act when it received data that the delta variant spreads as easily as chickenpox, can in rare occasions be spread by people who are vaccinated and is “likely” to cause more-severe illness, according to an internal CDC document obtained by The Post and detailed by Yasmeen Abutaleb, Carolyn Y. Johnson and Joel Achenbach.

Health officials were particularly concerned by data suggesting that vaccinated individuals with breakthrough infections of the delta variant have viral loads comparable to unvaccinated people infected with delta and thus may able to transmit the virus as easily as those who are unvaccinated.

CDC researchers analyzed a recent coronavirus outbreak in Massachusetts fueled by the delta variant and found good news and bad. The scientists discovered that three-quarters of the 469 people infected were fully vaccinated, a concerning finding that, in part, prompted the CDC to revise its mask guidance. But among all the cases, only five people were hospitalized (with four of them fully vaccinated), and there were no deaths, which demonstrates the efficacy of the vaccines and is a reminder that, as the researchers put it, “vaccination is the most important strategy to prevent severe illness and death.”

William Schaffner, medical director with the National Foundation for Infectious Diseases, agreed with the CDC’s revised guidance. “We don’t want to have vaccinated people become part of the transmission again,” he said.

– Does the kind of mask I wear matter?

The CDC’s general guidance for choosing an appropriate face covering has not changed amid the spread of the delta variant. The CDC still recommends masks with two or more layers of washable, breathable fabric and an adjustable nose wire to help with fit. There should be no gaps between the mask and your face, and your nose and mouth should be covered.

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But concerns about the delta variant and its ability to rapidly spread have prompted some experts to suggest that people should consider upgrading their masks to higher-quality face coverings, such as N95 respirators – especially people who are unvaccinated or are vaccinated but otherwise vulnerable. According to the internal CDC document, older individuals face a higher risk of hospitalization and death than younger people, regardless of vaccination status, The Post reported.

“Who would not want to reduce their inhalation dose of virus-laden particles by simply having everyone in an indoor space use good masks,” said Richard Corsi, an expert on indoor air quality and dean of the Maseeh College of Engineering and Computer Science at Portland State University. Corsi added that he has resumed wearing an N95 in indoor public spaces “because of the high transmissibility of covid-19 by the delta variant.”

– Do I need to upgrade to an N95 mask?

Not necessarily. At this point, there is no formal recommendation for the public, including those who may be more vulnerable to severe disease, to use N95s or other similar medical-grade respirators. What’s more, experts are split on the issue.

Recommendations to upgrade masks appear to be influenced by research that suggests the coronavirus can spread through aerosols, tiny particles that tend to linger in the air for much longer than the larger respiratory droplets that are also responsible for transmission.

“We can go a long way toward protecting the public by using higher-quality masks in indoor environments where mask-wearing is also required of all,” Corsi wrote. He noted that more effective masks, such as N95s, should be a priority for anyone who is not vaccinated.

Linsey Marr, an aerosol expert at Virginia Tech who studies airborne virus transmission, echoed the need for “highly protective masks along with everything else,” citing the delta variant’s transmissibility.

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“Where a simple cloth mask was helpful before, it’s not helpful enough now,” especially for those who remain unvaccinated, Marr previously told The Post.

On the other hand, Schaffner noted that many epidemiologists and infectious-disease experts think that the virus is primarily spread through infectious droplets – large and small – that can travel up to six feet in enclosed spaces. Standard surgical masks and well-fitted, multiple-layer cloth face coverings that meet the CDC’s standards have been shown to be effective at blocking these droplets, said Jaimie Meyer, an infectious-disease physician at the Yale School of Medicine. They also tend to be more comfortable than N95 masks.

“If people are concerned about the delta variant and they want to protect themselves, the answer is to get vaccinated,” Meyer said, “not to go get an N95.”

While there is disagreement over recommendations for higher-quality masks, experts said the decision to upgrade is personal and depends on various risk factors, including your health, the health of those you are in close contact with, community transmission rates and whether you’ll be in settings where the potential for exposure is higher.

Certain people, for instance, who are fully vaccinated but still vulnerable to severe disease may want to use an N95 and may be willing to wear it properly, Schaffner said. “On an individual basis, if you wish to really reduce your risk, you can do that,” he said.

If a fully vaccinated healthy person wants to wear an N95 mask, that would be “going the extra mile,” he added.

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– What are some pros and cons of using an N95 mask?

The efficacy of a mask is based on its fit and material. N95s are made of nonwoven, melt-blown polypropylene, Marr said. When fitted snugly to the face with no gaps around the edges, N95s can provide greater protection than looser surgical masks made of the same material because the fit ensures the respirators will filter at least 95% of airborne particulates, she said. It’s important, however, to make sure you use an N95 mask that has been approved by the National Institute for Occupational Safety and Health (NIOSH) and beware of counterfeit models.

Although the CDC still recommends that N95s be prioritized for health-care workers, the agency noted that as more respirators “become available they can be worn in non-healthcare settings.” But Meyer urged people to keep in mind that “it was not so long ago that we were in the midst of PPE shortages.”

And practically, Meyer added, N95s may not be the best mask choice for most people. For an N95 to function as designed, the respirator has to be properly fitted. Health-care workers, she said, regularly go through specialized fit testing.

“For someone to just go out and buy a box from Amazon just, to me, doesn’t make a ton of sense,” she said. “Just because you have a mask that is an N95 doesn’t mean that it will be appropriately fitted.”

When choosing a mask, it’s also important to consider comfort, said Erica Shenoy, associate chief of the infection control unit at Massachusetts General Hospital, and tightly fitted N95s can be difficult to wear for long periods of time.

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“You may have a mask that you kind of dread to wear or feels uncomfortable, or you’re constantly touching it because it’s not comfortable – and that also has downsides in terms of how effective the mask is going to be,” Shenoy said.

– What about KN95 masks?

KN95 masks, which are manufactured in China, can be equivalent to N95s in effectiveness. But they have not gone through the NIOSH approval process, and some experts caution that it may be more difficult to determine that the KN95 you’re using is high-quality. When N95s were in short supply, the Food and Drug Administration authorized some KN95s for emergency use by health-care workers, and you can refer to that list to find effective models.

– Can I still wear a cloth or surgical mask?

Yes – as long as it meets the standards set by the CDC and you’ve assessed that it’s the appropriate choice for you, experts said.

You can evaluate the efficacy of your mask with simple tests. A cloth mask should block light when held up to the sun or another light source, according to the CDC. You also shouldn’t be able to blow out a birthday candle with a mask on. For an extra layer of protection, some cloth masks also come with a pocket where a filter can be added.

If people are concerned or don’t know what mask to choose, Shenoy recommended seeking a professional opinion. “Ultimately, if they’re unsure that what they’ve chosen meets all those criteria or they think that they’re in a special situation where they need something more, that’s definitely a discussion to have with their clinician who knows them the best,” she said.

– Can I use a mask with an exhalation valve?

Masks that have exhalation valves or vents are not recommended, because they can allow virus particles to escape, according to the CDC.

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“Exhalation valves should always be avoided,” Corsi wrote. “This does not help to protect others around you.”

– Do I need to wear a mask outdoors?

While the revised CDC guidance does not say that fully vaccinated people need to wear a mask outdoors, the agency did note that they might choose to wear a mask in crowded outdoor settings if they or someone in their household is immunocompromised.

The risk of transmission outdoors is much lower than it is in indoor spaces where people are more likely to be crowded together and ventilation may be poor, Meyer said. It’s often easier to keep your distance from others outdoors, she said, and “there’s also the best airflow there could possibly be, and that allows the particles that contain the virus really to disperse so effectively.”

– How do I know whether my mask fits properly?

Make sure air isn’t leaking out of the top or sides of the mask. If you wear glasses and the lenses fog up when you have your mask on or your eyes feel dry, that may be a sign that the mask isn’t well-fitted and exhaled air is escaping from the top.

To improve the fit and protection of your mask, try adjusting the nose wire, using mask braces or double-masking, among other strategies. When layering masks, it’s recommended to wear a multiple-layer cloth mask over a surgical mask. Knotting the ear loops of a single surgical mask and tucking in the sides close to the face had a similar effect to wearing a double mask, according to the CDC.

– How should I care for my mask?

Cloth masks can be easily cleaned in the laundry or hand-washed with soap and water, according to experts and the CDC. Once masks are washed, they should be thrown in the dryer on the highest heat setting or air-dried.

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Surgical masks and N95s can’t be washed, so pay attention to the state of your mask. If there’s any visible signs of wear and tear, it’s time to get a fresh one.

Avoid using rubbing alcohol or disinfecting sprays to clean masks. “I have a surgical mask right in front of me, and if I were to spray that with some disinfectant, it would disintegrate,” Neysa Ernst, nurse manager in the biocontainment unit at Johns Hopkins Medicine, told The Post.

How frequently you wash or change out your mask depends on use and exposures. For example, you probably don’t need to wash or get a new mask if you’re wearing it only for a quick trip to the grocery store, Shenoy said.

Between uses, store your masks carefully and in a place where they can air out. It may help to expose the mask to sunlight, but too much sun exposure could be harmful, Jade Flinn, a nurse educator for the Johns Hopkins biocontainment unit, told The Post.

“We know that prolonged direct sunlight can degrade some of the plastic materials, even the foam in some of our surgical masks,” Flinn said.

When handling your mask, try to avoid touching the front and make sure to wash or sanitize your hands after you come in contact with it.

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– What else can I do to protect myself?

It’s important to take a layered approach to safety and consider your individual risk, experts said. “It’s not just about the mask,” Shenoy said. “It’s the situations that you find yourself in.”

If your age or health makes you more vulnerable to severe covid-19, avoid riskier situations, such as crowded public indoor spaces where you don’t know whether people around you are vaccinated or traveling to places were transmission rates are high, experts said. If you do have to be in those spaces, stay masked and try to keep your distance from others. Shenoy also suggested that vulnerable people socialize with others who are fully vaccinated.

“One of the primary interventions is to make sure the people that are in your household and your close contacts are all vaccinated to the extent possible, because that in effect acts like a cocoon for you,” she said.

While masks are again being deployed to help thwart the spread of the delta variant, experts emphasized that it’s critical to raise vaccination numbers.

“If all those people who weren’t vaccinated would just get vaccinated, then the circulation of this virus in our communities would really plummet,” Schaffner said. “But at the moment, they are permitting this virus to go out there, circulate and potentially expose even the vaccinated people.”