Making sure a mask fits snugly and use of two masks is likely to significantly reduce a person's exposure to the coronavirus, according to studies by U.S. Centers of Disease Control and Prevention (CDC) researchers.

In lab tests, they found wearing a cloth mask over a three-ply medical procedure mask, and knotting the ear loops of the medical mask so that it fits snugly and then tucking the excess material close to the face, helped reduce exposure to potentially infected aerosols by more than 90%.

In one experiment, an un-knotted medical procedure mask alone blocked 42.0% of particles from a simulated cough, and the cloth mask alone blocked 44.3%.

The double mask combination blocked 92.5% of the cough particles, they reported  in CDC's Morbidity and Mortality Weekly Report.

In an #AskReuters Twitter Chat , Dr. Charles Holmes, director of the Center for Innovation in Global Health at Georgetown University, recommended wearing the most effective mask on the inside. For example, he said, wear a surgical mask over a KN95 mask, or a cloth mask over a surgical mask.