Wearing a used mask can be less effective at protecting against coronavirus than not wearing one at all, a new study suggests.
Researchers looked at three-layer surgical masks, which are very common among healthcare professionals.
They found that, when new, these masks can filter out nearly three-quarters of tiny particles that linger in the air and are most responsible for infection.
But, when used more than once, they filter out just one-quarter of the minuscule droplets because the masks become deformed with each wear.
The team, from the University of Massachusetts Lowell and California Baptist University, says the findings provide evidence for why mask shape should be considered when examining their protection and designing new masks.
‘It is natural to think that wearing a mask, no matter new or old, should always be better than nothing,’ said co-author Dr Jinxiang Xi, an associate professor of biomedical engineering at UMass Lowell.
‘Our results show that this belief is only true for particles larger than five micrometers, but not for fine particles smaller than 2.5 micrometers.’
Three-layer masks are among the most recommended by health professionals to protect yourself and others from contracting COVID-19.
The inner layer is made from an absorbent material, the middle layers acts as a filter and the outlet later is made from a non-absorbent material.
For the study, published in the journal Physics of Fluids, the team developed a computer model of a person wearing a surgical mask with pleats.
Next, they looked at the behavior of aerosols, tiny liquid droplets and particles that can linger in the air.
The model tracked where aerosols landed on the mask and the face, and if they made their way into the the nose or lungs.
The tool showed that, when people wear masks, it changes the way that air flows around the face.
Researchers found that air does not enter through the nose and mouth at specific points, but rather through the entire mask surface at low speeds.
Next, they looked at the filtration efficiency of three-layer masks.