If the gold-plated surface is not designed to be in direct and prolonged contact with the skin, there is no problem; however, any surface intended for contact with the skin will be a possible source of nickel ions.

It is estimated that 20 per cent of all individuals with pierced ears who wear nickel-containing earrings will become nickel-sensitive.

Nickel adheres extremely well to base metals, much like other metals such as silver and gold adhere extremely well to nickel. Thus you will often find nickel as a base layer under gold-plated items.