Nickel-allergies
Many people get skin eruptions due to nickel-allergies when wearing jewellery made of white-gold. Nickel-allergies develop from absorbing nickel into your body constantly. But where does the nickel come from ?  
Nickel is a very wide-spread component of stainless steel-alloys, very often used in daily life, i.e. cooking-utensils, cutlery.....   

Therefore white-gold with a content of more than 0.5% nickel is forbidden in the European Community, for jewellery like rings, studs, chains and other pieces of jewellery, when directly in contact with the skin. For Studs, applied immediately after ear piercing the alloys should not contain more than 0.05 % Nickel.  
Also nickel-plated  jewellery is no longer allowed, if more than 0.5 micrograms/cm3/week could be absorbed by the skin.  
As a replacement some other alloys with less than 5% nickel or even nickel-free alloys have been developed.