The temporary skin discoloration that occurs after wearing certain jewelry or metal objects is a common experience. This greenish mark is not a sign of poor hygiene or a severe allergic reaction, but rather the result of a simple, superficial chemical process. The phenomenon is entirely harmless, washing away easily with soap and water. The discoloration results from a surface-level interaction between the metal and compounds naturally present on the skin.
The Metal Responsible for Green Skin
The metal most frequently responsible for leaving a green mark on the skin is copper. Copper is a reactive metal that readily interacts with its environment and is a popular material in jewelry, both in its pure form and as an alloy. The distinctive color transfer is not limited to pure copper pieces, as copper is often mixed with others to create harder, more durable materials.
Brass, an alloy composed primarily of copper and zinc, retains the reactivity of copper. Bronze, a mixture of copper and tin, will also cause skin discoloration under the right conditions. Even sterling silver, often used in high-quality jewelry, typically contains about 7.5% copper to increase its strength, allowing for a reaction. Gold jewelry below 14 karats often contains enough copper in its alloy to occasionally cause this discoloration.
The Chemical Reaction Behind the Color
The green color appears on the skin due to oxidation, where the copper metal loses electrons and reacts with surrounding substances. This reaction is accelerated by moisture and acidity, such as that found in human sweat, skin oils, and cosmetics. When copper atoms react with oxygen in the air, or with chlorides and sulfates present in perspiration, they form new compounds known as copper salts.
These copper salts are typically blue-green and include compounds such as copper carbonate and copper chloride. Once formed on the surface of the jewelry, these colored compounds transfer directly onto the skin. The acidity of an individual’s sweat can significantly influence the speed and extent of this corrosion process. Factors like diet, stress, and medications can alter the composition and acidity of sweat, making some individuals more prone to discoloration.
Practical Steps to Prevent Discoloration
Preventing the greenish stain involves creating a barrier between the reactive metal and the skin or reducing the environmental factors that promote oxidation. An effective method is to apply a clear sealant to the interior surface of the metal, such as a thin coat of clear nail polish or a specialized jewelry lacquer. This coating physically blocks the copper from coming into contact with sweat and air, halting the chemical reaction.
Another simple preventive measure is to keep the skin and the jewelry as dry as possible. Removing the item before showering, swimming, or strenuous physical activity limits exposure to the moisture and salts that accelerate corrosion. For frequent reactions, choosing jewelry made from non-reactive metals is the most reliable solution. Metals like stainless steel, platinum, titanium, or 18-karat and higher gold alloys contain little to no copper and are far less likely to cause discoloration.