Dr. Monica Gandhi, who coauthored the article with Marr, recommends that people who are more at risk of severe illness, work indoors around other people, or live in areas where COVID-19 transmission is high wear a cloth mask on top of a surgical one or insert a filter in between two cloth layers.

The idea has been hailed as common sense by Dr. Anthony Fauci, the nation’s top infectious disease expert. The CDC, meanwhile, has not made a recommendation on double-masking and did not respond to questions from BuzzFeed News.

Gandhi, an infectious diseases doctor and professor of medicine at the University of California, San Francisco, said people shouldn’t double-mask if they’re just going out for a walk in an area where they can still keep their distance from others. Double-masking is more important when indoors and in places where distancing is difficult, she added.