Face shape influences the most ideal mask fit
Joint research from Florida State University and Johns Hopkins University, both in the US, reveal how even the slightest facial asymmetry can affect mask fitting and protection. Using a novel analysis method called principal component analysis (PCA), and fluid dynamics, the researchers modelled adult faces to show the crucial importance of proper fit for all types of masks.
It is also indicated that double masking with improperly fitted masks may not significantly improve mask efficiency and produces a false sense of security. Masks with a less secure fit can cause more outward flow of air from gaps in the sides, top, and bottom; and while double layers increase filtering efficiency with a good mask fit, it could also lead to breathing difficulties.
“Facial asymmetry is almost imperceivable to the eye but is made obvious by the cough flow through the mask,” said Tomas Solano, from Florida State University. “[…] the only unfiltered leakage observed is through the top. However, for different face shapes, leakage through the bottom and sides of the mask is also possible.”
In realistic PCA simulations that integrated 200 adult male and female heads retrieved from data at Basel University in Switzerland, the slightest asymmetry in facial features were shown to be detrimental to mask fitting. For example, a cloth mask can have a tighter fit on the left side of the face than on the right side.
According to the US Centers for Disease Control and Prevention’s 2022 guidelines, loosely woven cloth masks offer the least protection against COVID-19, while N95 and KN95 masks offer the most protection.
The researchers suggest PCA-based simulations can be used to design masks with optimal characteristics for different populations by revealing general differences between male and female or child versus elderly facial structures and the associated air flow through masks.
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