I bought a box of N95 masks on Amazon to use (instead of my cotton cloth masks— that are apparently no longer cutting it against the Omicron variant).
The N95 masks are more difficult to put on than ones with ear loops .. and then there is the question of how many times they can be used before they should be discarded. (They cannot be washed in the washing machine).
The short answer: it depends. If the mask was used in a crowded place, or for a long time (say, 4 to 8 hours), it should probably be discarded.
[Infographic by John Blanchard for The San Francisco Chronicle]