14kt and 18kt gold are great metals for body jewelry. Gold, no matter the karat is not recommended for initial piercings because sometimes the fluids secreted by a healing piercing cause pitting of the gold. I found this out personally with a nipple piercing that would not heal properly. Once I changed to titanium it healed fast and I have never had a problem with it. Lucite and plexiglass are also used usually for ears and the balls on barbells.
Many people have the misconception that silver contains nickel which is indeed a toxic metal.
The reason silver shouldn't be used is that it corrodes when it comes in contact with sulfur which your body contains and this contact forms silver salt which is toxic. Gold plated jewelry is made by electroplating a thin layer of gold onto a base metal, usually aluminum. Gold filled jewelry is made by rolling a very thin layer of gold onto a base metal, usually stainless. But to get the gold to stick to the base metal they have to first underplate the base metal with either copper or nickel. The gold wears off exposing these base metals and they react with the sulfur in your body which can be toxic.