Armbrust gets many emails praising the comfortability and breathability of our masks. Some folks even attest to the longevity of how long they can wear them before swapping out for a new mask. According to the FDA, single use means just that. Once you put it on and take it off, you toss it.
Personally, I use about a mask a day. I believe it’s a good rule of thumb. But, it helps if we break down the science of how mask defense works. In 2006, a study was conducted that the fabric in masks that actually does the work of blocking out germs and particulate matter (like COVID-19) will only last for about 24 hours once a mask is worn.
In a sense, putting a mask on your face is when the countdown begins. The fabric inside masks is charged with static electricity. This static is what’s actually blocking all the harmful stuff, including viruses, from entering the body. After a mask is used, the static wears off, rendering it less than effective. The same principle applies to older masks. If you have a box of old masks laying around in a closet for upwards of two years, you should err on the safe side and get a new box.