Oh snap earring backs work on MOST earrings (post sizes differ by the millimeter). And they are solely recommended for small stud earrings (at the moment!).
Depending on how oily your skin/hair is, it's recommended to wash your oh snaps in soap & water or rubbing alcohol at least once a month. If you're a clean freak like me, you might wash them at least once a week, which is totally safe (yay food grade silicone!) :)
It's also always a good idea to clean (qtip + rubbing alcohol) your earrings and piercing holes #hygiene