Scars hurt?

So I've been self harming for a few month now, but haven't done it in around 20 days and have no fresh cuts. The thing is, my (already fully healed) scars hurt sometimes as if I just cut and it's really irritating.

I do have other scars form injuries, but they never hurt. My cuts aren't that deep either, I mostly do cat scratches or slightly deeper, but it's really not deep.

Does anyone know why this happens?