TL;DR: A green mark under a ring is almost always a chemical reaction between skin, sweat, and the copper content in lower-purity gold or costume jewellery alloys — not an allergy, and not a sign the ring is fake. Higher-purity gold (18ct+) and platinum rarely cause it because they contain far less reactive base metal.
What's Actually Happening
The green discolouration comes from a chemical reaction, not an allergic one: copper in the alloy reacts with acids in sweat and skin oils to form copper salts, which are green. This is the same basic chemistry behind a green patina on outdoor copper or bronze — just happening in miniature against skin.
Why Purity Matters So Much
9ct gold is only 37.5% pure gold, meaning over 60% of the alloy is other metals, often including a meaningful copper content. 18ct gold is 75% pure gold, leaving far less room for the reactive metals that cause staining. Platinum contains almost no base metal at all, which is why it essentially never causes this reaction.
Is It a Sign of a Fake or Low-Quality Ring?
No. Genuine, hallmarked 9ct gold can still cause this reaction — it's a function of purity, not authenticity. A green mark doesn't mean the ring isn't real gold; it means the alloy composition has enough reactive metal content to react with your specific skin chemistry.
Why It Happens to Some People and Not Others
Individual skin pH, sweat composition, and even the products used on the hands (certain lotions and sunscreens can accelerate the reaction) all affect whether and how quickly this happens. Some people wear the same 9ct piece for years with no reaction; others see it within days.
What to Do About It
The mark itself washes off with soap and water and isn't harmful. If it recurs consistently, the practical fix is moving to a higher purity — 18ct gold or platinum — rather than any treatment applied to the existing ring.
Choosing a Reaction-Resistant Metal at À Vie Diamonds
We work in 18ct gold and platinum as standard for exactly this reason — see our best metal for an engagement ring guide for the full comparison. Get in touch with any questions about metal choice.
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Frequently Asked Questions
Why does my ring turn my finger green? A chemical reaction between sweat, skin oils, and the copper content in lower-purity gold alloys, forming green copper salts — the same basic chemistry as patina on copper or bronze.
Does a green mark mean my ring is fake? No — it's about alloy purity, not authenticity. Genuine 9ct gold can still cause this reaction.
What metal never causes this? Platinum and high-purity gold (18ct and above) contain very little reactive base metal and rarely cause this reaction.
Last reviewed: July 2026 · À Vie Diamonds