The data collected are truly alarming - the population of nickel contact allergy patients is steadily growing and may already number approx. 1 billion people worldwide! Existing treatment regimens (based mainly on prevention and avoidance of exposure to nickel, which for some occupational groups is not even feasible) are failing and detailed testing of products for nickel content is not having the desired effect. Why does nickel contact allergy occur, what mechanisms drive it and why is it present in such a huge number of people?