I've got a hairline crack a couple feet long on the ceiling of my bathroom. Can I paint over it or do I need to patch it?

I'm thinking it was from mildew growing, which seems to be a fairly common problem in bathrooms. I cleaned the mildew off, and discovered the crack.

Is it a straight line? If so it’s a tape joint coming loose. I just built a house last year and the Sheetrock guy had to come back and redo my whole ceiling all the tape lines cracked ...luckily my contractor caught it before cabinets went up

If you paint over it, it will probably just reappear or it just won’t take the paint. Take the tape off, retape, joint compound(mud), light texture, paint.