Euro coins can cause bad skin reactions in people with nickel allergies, although some other coins containing comparable amounts of nickel, such as the Swiss franc, do not.
In a Brief Communication to last week’s Nature, Frank Nestle of the University of Zurich, Switzerland, and colleagues have come up with an explanation.
The two-alloy structure of one- and two-euro coins makes them prone to release large amounts of nickel in human sweat – as much as 320 times the quantity allowed under the European Union Nickel Directive, and even more than pure nickel does under the same conditions.
Nestle and colleagues show that it is the coins` central `pill` and outer `ring` design that is responsible for this enhanced nickel release.
The yellow and white alloys contain different amounts of nickel, copper and zinc, which encourages corrosion as metal ions flow from one alloy to the other during prolonged exposure to sweat – a process that eventually damages the coloration of the coins.
The rate of nickel release is roughly the same from the yellow and white parts, even though the former contains 80% less nickel.