(Reuters)

Making sure a mask fits snugly on the face and use of two masks is likely to significantly reduce a person’s exposure to the coronavirus, laboratory experiments described by U.S. health officials on Wednesday showed.

The U.S. Centers of Disease Control and Prevention (CDC) in January conducted experiments to see how well wearing a cloth mask over a three-ply medical procedure mask, and knotting the ear loops of a surgical mask and then tucking the excess material close to the face, protects against COVID-19.

They found that both these methods helped reduce the exposure to potentially infected aerosols by more than 90 per cent in laboratory simulations.

Results from one experiment demonstrated that the un-knotted medical procedure mask alone blocked 42.0 per cent of the particles from a simulated cough, and the cloth mask alone blocked 44.3 per cent.

The double mask combination blocked 92.5 per cent of the cough particles.

In another experiment, the CDC tried to simulate the spread of COVID-19 during breathing when one or both people are properly masked. In the first scenario with only the source of the aerosols wearing a mask, they found coronavirus exposure was reduced by 82.2 per cent when double-masking, and 62.9 per cent with a snug fitting, knotted and tucked surgical mask.

When the source and receiver of simulated breathing aerosols were both fitted with double masks, or knotted and tucked medical masks, the exposure of the receiver was reduced 96.4 per cent and 95.9 per cent, respectively, the experiments found.

The data underscore that a good, tight fit with no spaces around the sides or use of a second cloth mask to improve the fit of the first mask increases overall efficiency and reduces virus transmission risk, the CDC said.