Important findings of the study
The study found that wearing a used mask having low filtering efficiency can be riskier than wearing no mask at all. It also stated that masks help in protecting the upper airway the best from over 10-micron particles, while the face and lungs are protected from PM10 particles or particles that are smaller than 10 microns.
For the study, the team used a computational model where a person wore a three-layered pleated surgical mask, after which the team numerically tracked the particles through the mask, the report added.
Comparison of used mask with no mask
As the mask goes from a new one to an old one, it greatly impacts its efficiency to filter particles. The study found from its simulations that while a new mask was capable of filtering particles with an efficiency of up to 65%, after multiple uses, this figure could drop down to 25%.
The report quoted study author Jinxiang Xi as saying that the air is able to enter the mouth as well as the nose through a narrow region without a mask. On the other hand, if a mask is worn, the airflow can come close to the nose and the mouth through the entire face of the mask.
When a mask is worn, the airflow around the mask becomes slower, greatly bringing down the inspiratory airflow. This spreads the droplets over the surface of the entire mask, the report added. With slower airflows, droplets are more likely to be inhaled into the nose. This means the particles that go into the nose depend on the number of particles that actually manage to enter the mask, making filtration highly essential.
The study author was then quoted as saying that the study majorly found that a used mask having low efficiency in filtering out particles might not do much to protect the wearer, because when the efficiency falls below 30%, which can happen after two or three uses, more aerosols are likely to be inhaled.
Deposition of particles ranging between one and 10 microns in the lungs can be reduced by thrice the efficiency with the help of an efficient mask. The study also found that once the particles cross the mask, deposition in high concentration takes place in the pleats of the mask.