Environmental nickel pollution: does it protect against nickel allergy?

The Norwegian-Russian border area is polluted because of emissions from two local Russian nickel refineries. We patch tested the general adult population on both sides of the border. Only 7.2% of the Russian women were sensitized to nickel, compared with 27.5% of the Norwegian women. We suggest that long-term exposure to nickel may have induced immunologic tolerance in the Russian population.