The research Dr. Redfield cited included a newly published study suggesting that universal use of surgical masks helped reduce rates of confirmed Covid-19 infections among health-care workers at the Mass General Brigham health-care system in Massachusetts.

His comments are the clearest message yet from the CDC, amid fierce debate over facial coverings, fueled initially by shifting messages from federal and global officials about their necessity and then by those espousing individual liberties.

Researchers from around the world have found wearing even a basic cloth face covering is more effective in reducing the spread of Covid-19 than wearing nothing at all. And many are now examining the possibility that masks might offer some personal protection from the virus, despite initial thinking that they mostly protect others.

Experts caution that widespread masking doesn’t eliminate the need to follow other recommendations, like frequent handwashing and social distancing.

In the absence of widespread availability of N95 masks—considered among the most effective but typically reserved for health-care workers—transmission can still be reduced with simple and affordable face coverings, the research shows. In a study published last month in the journal Physics of Fluids, researchers at Florida Atlantic University found that, of the readily accessible facial coverings they studied, a well-fitted homemade stitched mask comprising two layers of cotton quilting fabric was most effective for reducing the forward spread of droplets. The research was conducted using a mannequin’s head, an air compressor and a smoke generator that mechanically simulated a cough.

The study found that aerosol-size droplets expelled from the mannequin with the double-layered cotton mask traveled forward about 2.5 inches on average, and that most of the leakage escaped from gaps between the nose and face. Loosely fitting facial coverings, including a folded cotton handkerchief with ear loops, as well as a bandanna were less helpful, the study found. With those masks, droplets traveled on average about 1.25 and 3.5 feet, respectively. In contrast, the study found droplets traveled about 8 inches on average with an off-the-shelf cone-shaped mask.

Meanwhile, droplets from an uncovered cough traveled around 8 feet on average, though the study found that they could travel up to 12 feet—double the currently recommended social-distancing guideline of 6 feet. Leakage from a common disposable surgical mask wasn’t studied, though two of the study’s authors, Siddhartha Verma and Manhar Dhanak, said they are working on it.

“It was surprising in a good way to see that a homemade mask could do so well…that we don’t have to get a very fancy mask,” Dr. Verma said. “A cotton mask can be washed at home and dried. Reusability is becoming important as we go into this for the long haul.”

They are also in the process of putting a laboratory apparatus together to test how much protection various masks might offer to the person wearing them.

The amount of virus exposure might influence degree of sickness, according to a review of viral literature and Covid-19 epidemiology by Monica Gandhi, a professor of medicine at the University of California, San Francisco. She and her co-authors posit in the research, expected to be published this month in the Journal of General Internal Medicine, that masks provide an important barrier and could lead to a milder infection or even prevent one altogether. While cloth and surgical masks can widely vary, she believes some masks can likely filter out a majority of large viral droplets.

Amy Price, a senior research scientist at Stanford’s Anesthesia Informatics and Media Lab, maintains, in contrast, that the primary benefit of wearing a mask is to protect others and reduce Covid-19 transmission. She believes that, excluding N95 masks, multilayered masks with a slightly waterproof outer layer best minimize spread. She said rubbing the outer layer of the mask with a latex glove before donning it creates static electricity—which Stanford researchers believe can better prevent virus particles from passing from the mouth to outside of the mask.

Researchers are hopeful that more evidence about the personal protection masks could lead to more use in coming weeks. The CDC said the use of cloth face coverings while in public in the U.S. increased to 76.4% in mid-May, compared with 61.9% in April, according to internet surveys sent to roughly 500 adults each month.

Some Americans who have resisted wearing masks have cited health concerns. However, leading medical groups said in a joint statement Thursday, “Individuals with normal lungs, and even many individuals with underlying chronic lung disease, should be able to wear a non-N95 facial covering without affecting their oxygen or carbon-dioxide levels.” Exemptions should be at the discretion of a physician, the groups said.

Researchers say the benefits of widespread mask use were recently seen in a Missouri hair salon, where two stylists directly served 139 clients in May before testing positive for Covid-19. According to a recent report published by the CDC, both wore either a double-layered cotton or surgical mask, and nearly all clients who were interviewed reported wearing masks the entire time.

After contact tracing and two weeks of follow-up, no Covid-19 symptoms were identified among the 139 clients or their secondary contacts, the report found. Of the 67 who were willing to be tested, all were negative for Covid-19.

According to recent projections from the University of Washington’s Institute for Health Metrics and Evaluation, the Covid-19 death toll in the U.S. would rise to more than 224,000 by Nov. 1. The number is based on expectations that Covid-19 mandates will continue to be eased until rising cases prompt shutdowns again in some places. Almost 140,000 people have died from Covid-19 in the country so far, according to data compiled by Johns Hopkins University.

Yet if 95% of the U.S. population began wearing masks, the expected death toll would drop by more than 40,000 cases to about 183,000 people, according to IHME.

Wearing a mask is “one of the most urgent things we can do to get our country under control,” said Melanie Ott, director of the Gladstone Institute of Virology. “We’re all waiting for the vaccine, we’re waiting for therapeutics, and we’re not there.”

“We have masks, we have social distancing, and we have testing,” she continued. “But there’s not much more in the toolbox here.”

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