Recently, various health systems, including the Centers for Disease Control and Prevention (CDC), contended that the public will have to continue wearing face masks even after they receive a targeted vaccine for COVID-19.
Unfortunately, not all masks offer the same degree of protection. Similarly, how you clean and wear your face masks further influence their utility.
According to a new paper published in the Physics of Fluids journal, researchers from the University of Massachusetts Lowell and California Baptist University determined that wearing a mask with low filtration efficiency can actually be worse than not wearing one at all.
N-95 masks (without valves), and double-layer cotton offer the most protection, assuming they are properly washed after each use. The CDC suggests washing masks in a washing machine or by hand.
If using a washing machine, the agency reports that including them with regular laundry is fine— with standard laundry detergent and the warmest water the cloth material of your mask can endure.
Surgical masks however offer less protection the older they are. The authors of the new report found that the filtration efficiency of the three-layer surgical mask can vary from 65%, if new, to 25% after one use.
Airflow speed is also determinative of a mask’s ability to filter out viral debris. Lower speed near the face facilitates the inhalation of aerosols into the nose.
“It is natural to think that wearing a mask, no matter new or old, should always be better than nothing. Our results show that this belief is only true for particles larger than 5 micrometers, but not for fine particles smaller than 2.5 micrometers,” said author Jinxiang Xi. “We hope public health authorities strengthen the current preventative measures to curb COVID-19 transmission, like choosing a more effective mask, wearing it properly for the highest protection, and avoid using an excessively used or expired surgical mask.”
The authors additionally gauged how effective wearing a three-layer surgical mask against inspiratory airflows.
To do so, a computational face mask model was developed using a physiologically realistic model of a person wearing a surgical mask with pleats. This was paired with numerical values designed to track how easily particles pass through these masks.
More directly, how aerosols pass through various masks, the face, respiratory airways, and the nose, pharynx, and deep lung.
SARS-CoV-2 particles evidence an average diameter of 0.1 micrometers. In aerosols, these particles remain active for roughly three hours.
A four-layer cotton muslin mask can reduce the contamination of all particles by 99%.
Single layers of scarfs, sweatshirts, T-shirts, and towels were associated with a filtration efficiency of 10% to 40% in experiments testing, so it’s important to layer up if you’re using a makeshift mask out of any of these materials.
A single layer of fabric like cotton-flannel can stop over 90% of active viral particles. The data changes with some frequency but the protective utility of cloth in regards to viral infection has been consistent across studies using both human and animal models alike.