Gold itself is inert, and does not typically react with skin to cause discoloration. But there are certain conditions under which gold jewelry can affect the color of your skin. Other metals are often added to gold in order to harden it or change its hue, and these metals may be responsible for the discoloration.
Contact dermatitis is an allergic reaction in which the surface of your skin becomes discolored or develops a rash, due to contact with an allergen. According to PubMed.gov, studies indicated that gold is a common allergen that can induce dermatitis on the face and eyelids, as well as on areas of the skin where prolonged contact occurs. The study concluded that just under half of the subjects who experienced contact dermatitis due to skin exposure were found to be reacting from another documented allergen within the gold alloy.
If your skin is naturally acidic, it may react with the copper used in gold jewelry to create a green discoloration on the skin. This discoloration is more common under humid conditions, or when high heat causes you to sweat. This acidity can cause a chemical reaction within the copper that simulates oxidation, which creates a green color in copper. If your skin turns green from gold jewelry, remove the jewelry and wash your skin. To avoid this side-effect of gold jewelry, only wear higher-quality and more pure gold, such as 18-karat gold.
Nickel reacts with skin similarly to copper, but it turns black instead of green. Nickel is commonly used in lower-quality gold jewelry, and as a base within gold-plated jewelry. If the softer gold plating wears off over time, your skin can become exposed to the nickel beneath and cause this discoloration.
Skincare-News.com notes that other factors may contribute to skin discoloration due to gold. Many medications, such as antibiotics, can cause a discoloration of your skin where it makes contact with jewelry. Residue from soaps, cleansers, lotions and detergents can also build up and cause an allergic or chemical reaction, which discolors the skin.
According to ChainzOnline.com, skin discoloration due to gold is sometimes attributed to iron deficiency or anemia. This article dismisses a direct correlation between iron and this type of discoloration but notes that the iron levels in your blood may affect your body's pH level. If your pH becomes more acidic, a reaction due to copper or nickel within a gold alloy can occur.