Earwax, boogers, toenail fungus — the body can be pretty gross sometimes. Don’t forget to add “belly-button gunk” to that list. And when you see something in there, you probably want to get it out.

A complication with belly button piercings is rejection, or when your body tries to remove the piercing from your skin. This is an immune response—your body sees the piercing as a foreign object and ...