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Gold has a reputation for being chemically untouchable. But according to Western University chemist Yolanda Hedberg, that reputation is a little misleading—gold is not unreactive so much as selective about what it reacts with.

"Every material has its own enemy. Its own kryptonite," said Hedberg, Canada Research Chair in Corrosion Science. "For gold, one of those enemies is sulfur."

That distinction helps explain what Hedberg and her collaborators at Surface Science Western and the University of Copenhagen found when they tested five pairs of 10K and 14K gold earrings purchased from a jeweler.

After a week in cysteine-modified artificial sweat, all five pairs released measurable amounts of gold. Cysteine is an amino acid, or protein building block, made naturally by the body that contains sulfur, which binds to gold.

The amounts were tiny, and the findings do not show that the released gold is enough to cause an allergic reaction. But the study, published in the journal Contact Dermatitis, demonstrates that gold in jewelry can become chemically available under the right conditions—a finding that helps explain how exposure to gold can occur at the skin.

Gold, silver and platinum are known as noble metals because they do not readily react with oxygen. That resistance to oxidation is a big part of gold's reputation for stability. But, Hedberg says, it does not mean the metal is universally unreactive.

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