Why jewellery turns skin green

The colour of a new penny

When the Statue of Liberty was completed in 1886, she was not green at all. The US National Park Service, which looks after her, describes her original colour as a traditional brown, like an American penny. Her skin is copper, about 2.5 millimetres thick, and over roughly thirty years it oxidised into the soft sea green we know today.

A ring that leaves a green band on your finger is doing the same thing on a very small scale. The colour is not coming from your skin. It is coming from the metal, and in almost every case the metal is copper.

What the green actually is

The Royal Society of Chemistry puts it simply: copper reacts with oxygen in the air and with your sweat to form a compound with a green tinge, which can then rub off onto your skin. The green film is known as verdigris, and it brushes off easily.

Sweat is not the only thing the metal meets. A dermatologist writing for Nebraska Medicine, a US health system, explains that the copper in jewellery can also react with lotion and other products on the skin. She adds that the same thing can happen with other metals, just less often.

The reassuring part comes from the same dermatologist: the green residue is not harmful, and it washes off with soap and water.

Where the copper comes from

Copper turns up in a lot of jewellery, often where you might not expect it. Pure silver and pure gold are too soft for most everyday pieces, so they are mixed with other metals, which the UK Assay Offices say are added for strength, durability and colour. Copper is one of them.

With gold, the carat makes a real difference. 18 carat gold is three quarters gold. 9 carat is 375 parts in 1,000, so most of the metal is something else. According to the World Gold Council, copper is what gives rose gold its pink, and its typical recipes for yellow gold include copper too. White gold is usually alloyed with white metals such as palladium or silver instead.

Sterling silver has copper in it as well. The Sheffield Assay Office describes sterling as an alloy of silver and base metals such as copper, and notes that the copper reacts with sulphur in the air as part of ordinary tarnish.

When plating wears through

Some jewellery that looks like gold or silver is copper, or a copper alloy, with a precious metal on top. The Nebraska Medicine dermatologist describes exactly this: while the outer layer is intact, the copper stays covered. Once it wears off, the copper beneath can react with sweat and lotion, and the green appears.

Plating is thin. Under the UK Assay Offices' guidance, the gold on gold plated silver should not be more than 2 microns thick, which is two thousandths of a millimetre. The inside of a ring, which rubs against the finger all day, is usually where a coating gives way first.

In the UK, the words on the label can help. "Gold plated silver" means gold over silver, and it is hallmarked as silver, not gold. "Gold tone" and "gold coloured" describe a colour only, and tell you nothing about the metal underneath.

A stain or a rash?

A green mark and a skin reaction are different things, and it helps to tell them apart. The green is a coloured deposit sitting on the skin. A reaction is the skin itself becoming irritated or inflamed.

If washing the green away leaves skin that is itchy, blistered, dry or cracked, that is a different matter. The NHS says avoiding whatever triggers contact dermatitis is the key, so stop wearing the piece. The NHS suggests speaking to a pharmacist if contact dermatitis is troubling you, and seeing a GP if the symptoms are persistent, keep coming back or are severe.

Stopping it happening

There is no single fix, but a few simple steps make a mark much less likely.

• Choose a metal with less copper. Higher carat gold has less room for other metals, and fine silver and fine gold are almost pure.
• Have worn plating renewed. If the gold or silver layer has worn away, a jeweller can re-plate the piece and cover the copper again.
• Add a clear barrier. The Nebraska Medicine dermatologist suggests a coat of clear nail polish on the part that touches the skin. It needs reapplying every so often as it wears.
• Keep sweat and lotion away from it. They are what the copper reacts with, so it makes sense to let hand cream soak in before putting rings on, and to take pieces off for exercise.
• Keep jewellery dry. The Sheffield Assay Office advises keeping silver you don't often wear in dry conditions, because moisture speeds up tarnish.

Cleaning skin and jewellery

For your skin, soap and water is all it takes. The mark sits on the surface and washes off.

For the jewellery, go gently. The Sheffield Assay Office recommends light cleaning with a specialist silver cloth, and cleaning silver as rarely as you can to avoid wear. It warns that household remedies such as aluminium foil, baking soda, toothpaste and vinegar can cause long-term damage if used often. On plated pieces, gentleness matters even more, because every rub takes a little of a very thin layer with it.

Back to the penny

There was once talk of returning the Statue of Liberty to her original brown. Engineers argued that the green was protecting the copper, the Royal Society of Chemistry notes, and so it stayed. A ring is a different matter: you probably don't want it leaving its signature on your finger. But the cause is the same honest piece of chemistry, a little copper meeting air and sweat, and once you know where the copper is, the green is easy to keep at bay.