Do you know about any studies of adults wearing one and the same mask for 8 hours straight? School children in my country are required to wear them for a whole day, and none of them replaces them throughout. I could only find studies about medical personal wearing them at most (!) for 2 hours, and then they took a break and changed their mask. Masks are a hygienic product. Using a hygienic product for longer than it's meant to is a health hazard, and disgusting. You are not meant to wear a tampon for a week. You are not meant to reuse a condom for a second time. You are most certainly not meant to pull a condom over your penis after it already started to dry. After hours, your nose and mouth excretions will start to dry and accumulate on the mask. Tasty.