Gold jewellery can contain nickel, depending on the type and composition of the gold. Gold is often alloyed with other metals to make it stronger, and these alloys can contain nickel.
The proportion of nickel in a piece of gold jewellery can vary widely, ranging from almost none to as much as 20%. In addition, some gold plating processes use nickel as one of the base layers, which means that the finished product may still have traces of nickel.
If you're allergic to nickel and want to wear gold jewellery, read the label carefully or ask your jeweller for more information about what metals are present in the jewellery you're considering buying.