Metals That Cause Reactions and Irritations

Many metals aren't recommended for initial body piercings because they often cause skin irritation and allergic reactions. Among these metals are brass and bronze, the alloys of both vary widely and may cause irritations or negative reactions.

Additionally, copper, zinc and iron are not recommended for piercings, as they can be reactive. Nickel jewelry is a well-known cause of allergic reactions in many people. In fact, some European countries have regulated piercing jewelry, now requiring it to be less than 0.05 percent nickel.
Metals That Don't Mix With Body Fluids

Some metals aren't recommended for first piercings because of how they react with body fluids and body tissues. Gold plated jewelry, for example, isn't recommended because the plating can rub off and expose an underlying metal that reacts with your body.

Also, avoid fake gold jewelry made from other base metals, since they could contain unknown base metal and may corrode when exposed to body fluids.

Lastly, sterling silver oxidizes when it contacts body tissues and fluids. Silver jewelry can often be safely worn in healed piercings, but it should never be worn in initial unhealed piercings.
Other Metals to Avoid

Some metals should be avoided for other reasons. Take gold filled jewelry, which isn't recommended for piercings because it could contain unknown base metals, and it's unclear how your body would react to them. 

Although 24k gold is often praised because it is the highest grade of gold, it should be avoided for piercings because it is generally too soft for jewelry. As a result, it will be easily damaged, not lasting for the long run.

Finally, non-stainless steel is not recommended for piercings. Instead, use surgical implant grade stainless steel. Also, avoid steel claiming to be "surgical steel," which is not verified as "implant grade surgical steel."