After months of demands for federal health officials to update mask recommendations, the Centers for Disease Control and Prevention announced new guidelines Wednesday that include wearing well-fitting face masks or two masks at a time to help curb the COVID-19 pandemic.

The updated guidance follows the release of new research from the CDC which tested various masks in a lab setting and found evidence that combining a cloth mask over a surgical mask could dramatically reduce both the spread of the virus to others and exposure to the virus oneself.

The CDC’s new recommendations advise Americans to select masks with a nose wire that can be adjusted for a snug fit, and to use a mask fitter or brace to better seal their masks. The CDC also recommends wearing a mask with multiple layers for greater protection, or layering a cloth mask over a disposable medical mask. 

For a better fit, it advises knotting the ear loops of the disposable mask and then tucking and flattening the extra material on the sides.

The CDC says it does not recommend wearing two disposable masks at a time. And it says there is no need to layer another mask with a KN95 mask, the commonly-used alternative to the professional-grade N95 masks used by health care workers and first responders.

“I want to be clear that these new scientific data released today do not change the specific recommendations about who should wear a mask or when they should wear one. But they do provide new information on why wearing a well-fitting mask is so important,” CDC Director Rochelle Walensky said at a White House COVID-19 briefing.

For the new study, CDC researchers tested combinations of multi-layered cloth and common surgical or medical procedure masks in a laboratory, simulating breathing and coughing between pairs of dummies.

When only a disposable mask was worn, just 42% of cough droplets were blocked in the experiment. Combining the disposable mask with a cloth mask on top blocked 92.5% of particles expelled from the cough.

Combining the two masks also reduced the wearer’s “cumulative exposure” by 83% from droplets spread by an unmasked source, the study reported. That number rose to 96.4% if both dummies were fitted with double masks.

“The data in this report underscore the finding that good fit can increase overall mask efficiency. Multiple simple ways to improve fit have been demonstrated to be effective,” the researchers wrote.

The new research comes after months of pleas by advocates for the CDC to update its guidance to include recommending wearing two masks, after other studies and anecdotal evidence suggested the move could curb the spread of the virus. The agency’s top officials had declined to change their official recommendations until this new research had been completed, though many — from President Biden to Dr. Anthony Fauci — had already been spotted wearing two masks.

In other countries, a handful of health authorities have directed citizens to move away from cloth masks altogether in favor of single-use, high-filtration masks. Germany’s government mandated “medical masks,” like surgical or KN95 masks, in public transit and stores last month.

The CDC’s announcement comes amid fears of a potential surge in new cases from more infectious virus variants now circulating in the United States. The agency had previously predicted the fast-spreading B.1.1.7 strain of the virus, which was first identified in the United Kingdom last fall, could become the dominant strain here by March.

“We should not despair at that because there are things that we can do to prevent that. It is not outside of our power to do that,” Dr. Fauci, President Biden’s chief medical adviser for the pandemic response, said Wednesday.

Contact tracing of some previous cases of the virus variants in the United States revealed that its spread was being fueled by people merely not wearing masks and holding in-person gatherings, the CDC has said.

“The two things that we can do are some of the things that Dr. Walensky just mentioned: searing of masks, avoiding congregate settings, keeping your distance, and washing your hands together when vaccine becomes available to you, to please get vaccinated,” Dr. Fauci said.