Piercings in Islam: What's Permitted?

As-salamu alaykum, I've been wondering about getting piercings that are discreet, like on my lower back, belly, or helix. Since I dress modestly, they wouldn't be visible to anyone, not even my mahram. I'd love to know if such piercings are halal, considering they won't be seen by non-mahram men or women. Jazakum Allahu khayran for any guidance.