Though these masks were originally designed to be disposable after a single use, they can be reused. The CDC recommends that you should reuse an N95 or similar mask no more than five times, though it could be more depending on how long you've worn the mask during a given day and under what circumstances.  Russo (and other experts PopSci has consulted) recommends that people rotate their masks out. One way to do this is to wear a new mask each day of the week. After a week, any viruses and bacteria on your mask will be dead, so it's safe to wear these same masks on the same days of the next week. One way to do this is to keep used masks in separate, numbered paper bags when you are not wearing them. You can even number the masks themselves or mark them for each day of the week.  That said, Marcozzi says that within reason, you can keep reusing masks for "multiple days" beyond the five times the CDC recommends as long as they look clean and undamaged on the inside and are not noticeably wet. If you've worn a mask long enough to stretch the ear loops out, he says, you need to replace it to get a good fit. You should never wash these masks; it will destroy them.