The most common reason why gold jewelry discolors and turns skin black is "metallic abrasion" which is caused by the presence of make-up on skin or clothing. Many cosmetics contain compounds which are harder than jewelry itself, which wear or rub off tiny particules. If you took a moment to examine fine particles you would see that it looks like jet-black-dust and when this "dust" comes in contact with absorbent surfaces such as skin or clothing, it sticks and forms a black smudge.

One of the easiest ways to prevent discoloration of gold jewelry due to metallic abrasion is to simply change the brand of cosmetics you purchase to a brand which is less abrasive. If this is not possible, try removing rings and other jewelry while applying cosmetics and thoroughly wash areas of skin which come in contact with cosmetics with soap and water before putting your jewelry back on.

Another reason why gold discolors is actual corrosion of the metals that are mixed with gold to make it more durable. Pure gold does not corrode, however the alloys that are commonly mixed with gold such as copper and silver do corrode with exposure to certain chemicals. When this occurs, the result is the formation of very dark compounds which can stain the skin and discolor gold. For this reason, jewelry should be removed when working with harsh chemicals.

The fats and fatty acids released by our bodies when we perspire can also cause a chemical reaction with the alloys mixed with gold, thus we are more likely to discolor our gold jewelry and create black marks on the skin beneath jewelry when we wear our jewelry during rigorous activities. This problem can worsen in seacoast and tropical areas where chlorides combine with perspiration to form a corrosive element which can discolor skin. Smog fumes have also been known to attack the alloys used in the production of jewelry and can rub off on our skin. Frequent cleaning of your jewelry with an appropriate cleaning solution helps to remove perspiration and dirt particles which will reduce the effect. People who perspire easily might consider using an absorbent powder which is free of abrasives on skin which comes into contact with their jewelry.