Many people wear copper bracelets because of their beauty and alleged healing properties, but after you wear one for a while, the skin beneath the copper turns green. The color change occurs as a normal reaction to the prolonged copper exposure on the skin, typically caused by oxidation. The green color fades when you stop wearing the copper, and it is not harmful to your health.

As an element found naturally in the earth, copper requires refining into the metal worn as jewelry and used in kitchenware and wiring. Copper’s ability to conduct electricity with minimal loss of energy makes the metal extremely valuable. When exposed to other chemicals or outside elements, even those as simple as oxygen, copper reacts, leading to changes on its surface.

The most commonly seen chemical reaction that occurs to copper includes oxidation. When copper gets exposed to air, it results in the copper's surface darkening. When that surface is also exposed to saltwater, as with the Statute of Liberty in New York Harbor, the copper turns bluish-green. This is like its reaction to prolonged contact with your skin. The formula for copper oxidation: 2 Cu + O₂ → Cu₂O.

The acidic nature of human sweat and other chemicals on the skin, such as soaps, lotions and makeup, react with the copper. This reaction causes a green patina or surface coating to form on the copper, and that color gets transferred onto the skin. The reaction varies according to individual body chemistry, both in how long it takes for the green discoloration to form and in how distinct the color becomes. Some people might not experience any discoloration at all.

Although skin acidity might seem like a drawback when dealing with jewelry, research by the San Francisco Veteran's Affairs Medical Center shows that the acidic nature of skin plays a part in holding the skin surface together, as well as strengthening it and protecting your body from disease.

Copper bracelets can be copper all the way through, or they might be formed from another, usually less expensive metal and simply have a copper-plated layer on the outside. Both types of bracelet can cause the same reaction, but copper-plated bracelets might eventually wear through the copper plating on the inside--particularly if you clean them frequently -- leaving the underlying metal, rather than the copper, exposed to the skin. This might eliminate the skin discoloration unless the underlying metal also is oxidation-prone, such as nickel.