Metals and materials used are listed in the item's description of each piece.
The bulk of our jewelry is made with 316L steel or 6AL4V ELI F-136 titanium which will not tarnish or rust and considered hypoallergenic.
For most people steel is just fine, but if you have had reactions before to steel or have a severe nickel allergy it is best to stick with titanium.
Some pieces (mostly dangles and charms) are plated over brass/alloy which is durable but body oil, lotions, etc can wear the plating over time. Keeping the brass plated jewelry clean and away from chemicals will keep the jewelry from tarnishing. Pieces using brass are also listed in the item's description.
It is always recommended to keep your initial jewelry in your piercing until it is fully healed before switching to a new style.