A team of scientists from the University of Massachusetts Lowell and California Baptist University carried out a study to explain that not all masks protect the same from Covid-19 transmission.

They stated in their study, published in the journal Physics of Fluids, old masks may be worse than not wearing a mask at all.

These findings will likely influence the guidance on mask-wearing and potentially mask design, the researchers speculated.

For the study, the team created a computational face mask model to predict how masks impact the inhalation and deposition of airborne particles in the upper respiratory tract.

The team added a surgical mask with pleats to the model and tracked the particles moving through the mask with numerical methods.

Results

The findings of their modeling suggested that the mask altered airflow around the face, forcing it to enter the nose and mouth through the entire mask rather than through specific paths.

The air movement into the airways was much slower through the mask than it usually is. This reduction in airflow speed enhanced the inhalation of aerosols into the nose, the researchers found.

They concluded that, even though masks filter out a large number of particles, those that escape the mask’s filtration are allowed to enter the respiratory tract.

Their results suggested that a three-layer surgical mask can achieve filtration efficacy as high as 65 per cent (if new) and as low as 25 per cent (if old). It further added that wearing a mask with a 25 per cent filtration efficacy may be worse than going without.

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