Surgical steel is something of a mystery metal; there are roughly 450 different mixes that qualify as surgical steel. Pretty much all of them carry some content of nickel. Nickel is a known sensitizer (people become more sensitive through contact).
As we tell many of our clients: There are risks to breastfeeding your baby with nipple piercings, however, they can be reduced or eliminated with careful planning. The most common risks to your infant from pierced nipples include leaking milk (creating too fast a flow), obstructed ducts leading to lowered milk supply, latch difficulties, damage to the baby’s mouth, and/or choking from jewelry that is not removed.