**Core Concept**
Contact dermatitis is an inflammatory skin reaction caused by exposure to allergens or irritants. In sensitive individuals, certain materials used in jewelry can trigger this reaction. Common culprits include metals, dyes, and other substances that come into contact with the skin.

**Why the Correct Answer is Right**
Nickel is a well-known allergen that can cause contact dermatitis in sensitive individuals. When nickel comes into contact with the skin, it can penetrate the outer layer and trigger an immune response, leading to inflammation and skin irritation. This is because nickel binds to keratin, a protein found in skin cells, and causes an immune reaction.

**Why Each Wrong Option is Incorrect**
**Option A:** Copper is not typically associated with contact dermatitis, although it can cause skin irritation in some individuals. However, this is less common compared to nickel.
**Option B:** Gold is generally considered hypoallergenic and is rarely associated with contact dermatitis.
**Option C:** Silver is also considered hypoallergenic and is not typically a cause of contact dermatitis.

**Clinical Pearl / High-Yield Fact**
Remember that nickel is a common allergen that can cause contact dermatitis, and individuals with a history of nickel allergy should avoid wearing jewelry made from this metal.

**Correct Answer:** C.