The Centers for Disease Control and Prevention on Friday updated its guidance on masks for the general public, now saying that people "may choose" to wear N95 and KN95 masks because they offer the best protection against Covid-19.
But the agency stopped short of saying that people should opt for certain masks instead of others, saying that the "CDC continues to recommend that you wear the most protective mask you can that fits well and that you will wear consistently."
Previously, the CDC did not recommend that the general population wear N95 masks or KN95s, a similar type of mask made in China, fearing that a run on those higher-quality masks would impact the supply in health care settings. The CDC now says shortages are no longer a concern.
"When worn consistently and properly," the agency wrote on its website, N95 respirators approved by the National Institute for Occupational Safety and Health, or NIOSH, "provide the highest level of protection from particles, including the virus that causes Covid-19."
Some public health experts said the guidance was long overdue and doesn't go far enough.
"We really need to go a step further and say this is the standard we should be aiming for," said Dr. Ranu Dhillon, a global health physician at the Harvard Medical School and Brigham and Women's Hospital.
He said it should be easy for most people to find comfortable "N95-caliber" masks so they can wear them in high-risk indoor settings, such as crowded shops and hospitals.
"CDC should have come out in front of this two years ago," he said. "The science was clear two years ago."
Tara Smith, a professor of epidemiology at the Kent State University College of Public Health in Ohio, said that while the CDC guidance is welcome, she has concerns about how people who need high-quality masks such as N95s would have access to them.
"Is there a plan to distribute them, especially for folks who can't afford them or can't easily find them? This was something I hoped would be done earlier this year, but still nothing," she wrote in an email. "Recommendations are great, but without access, especially for those at highest risk, it's not enough."
On Thursday, President Joe Biden said his administration is planning to make "high-quality" masks available to the public at no charge, but declined to offer details.
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The CDC said in its updated guidance that it "continues to recommend that you wear the most protective mask you can that fits well and that you will wear consistently."
A mask should fit close to the face without any gaps, and be comfortable enough to wear for long periods of time when needed, it said.
The agency did, however, offer a ranking of commonly used face coverings in order of highest to lowest protection, with N95s approved by NIOSH and KN95s at the top.
Disposable surgical masks were next on the list, however the CDC advised making sure they fit properly. The agency now recommends double masks in this scenario: Wearing a cloth mask over a disposable surgical mask can help it fit more snugly against the face.
"Loosely woven cloth products provide the least protection," the CDC said. Cloth masks should include multiple layers of tightly woven fabric. The fabric should block light when held up to a bright light source.