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What’s the deal with shifting guidance on masks during the coronavirus pandemic?

A commuter wore a face mask while departing Nubian Station in the Roxbury neighborhood of Boston on April 29.Craig F. Walker/Globe Staff

Guidance on masks has shifted during the COVID-19 pandemic, with experts initially saying they were largely unnecessary before reversing course and advising people to don face coverings whenever they can’t practice social distancing.

So what changed?

An entry on the CDC website suggests the recommendation on masks evolved as researchers learned more about the potential for asymptomatic coronavirus carriers to unknowingly spread the disease to others.

“We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms ('asymptomatic’) and that even those who eventually develop symptoms (‘pre-symptomatic’) can transmit the virus to others before showing symptoms," site says. "This means that the virus can spread between people interacting in close proximity—for example, speaking, coughing, or sneezing—even if those people are not exhibiting symptoms.”


The site says face coverings in public are now recommended in “light of this new evidence.”

A key development came April 3, when federal officials urged everyone to wear “non-medical cloth” face coverings outside their homes to curb the spread of coronavirus, after weeks of advising most Americans there was no need to wear protective face masks.

“This is voluntary,” President Trump told reporters at the White House, after announcing the updated recommendation. “I don’t think I’m going to be doing it.”

Prior to April 3, the Centers for Disease Control and Prevention had advised that only those who were sick — or caring for a sick person — wear a face mask, in light of the shortage of available masks.

In late February, the US surgeon general was more blunt. “STOP BUYING MASKS!” Surgeon General Jerome M. Adams, wrote on Twitter. “They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!”


That advice changed in early spring when the CDC, in a draft document first reported by STAT, recommended that Americans start wearing homemade face masks, reserving medical-grade masks for health care workers.

Wearing face coverings in public would mainly serve to keep the wearers from spreading the coronavirus, federal health authorities said in the April 3 announcement.

Prior to that announcement, federal officials had advised against face masks largely out of concern that people would buy up gear essential for health care workers; false assurance that they would be fully protected and wouldn’t also engage in social distancing; and concerns that people could infect themselves by constantly touching their faces to adjust the masks.

Currently, however, the CDC website endorses the use of masks, while emphasizing that social distancing “remains important to slowing the spread of the virus.”

The site says the agency “recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies) especially in areas of significant community-based transmission.”

Massachusetts went all-in on masks May 1, when Governor Charlie Baker issued an order requiring people to cover their nose and mouth if they’re unable to keep a six-foot distance from others in any “place open to the public.”

The state requirement for a face covering — which can range from a bandanna or T-shirt to a homemade, disposable, or professionally made mask — does not apply to children 2 years old and younger or those with medical issues that would prevent them from wearing a mask.


The CDC advises the same exemptions, stating on its website that “children under age 2, or anyone who has trouble breathing, is unconscious, incapacitated or otherwise unable to remove the mask without assistance” should not wear face coverings.

Joseph Allen, a professor of exposure assessment science at the Harvard T.H. Chan School of Public Health said in a media briefing last week, “Just like you don’t leave the home without your phone and wallet these days, you shouldn’t leave the home without a mask and some hand sanitizer. Universal mask wearing should happen. It’s supported by the scientific evidence.”

Allen has argued there are multiple reasons to do it, including stopping infected people from spreading the virus, getting some protection from people who have the virus, and as a reminder to people not to touch their faces.

“So we need to be doing this," he said. "If you’re at a park ... and separated from others, it’s OK to pull your mask down. If you’re near other people or if you’re passing people on the sidewalk or certainly if you’re at a store, you should be wearing a mask.”

David Abel, Martin Finucane, and Matt Stout of the Globe Staff contributed to this report.

Travis Andersen can be reached at