What you describe sounds like black dermographism. It’s not an allergy.

Black dermographism is usually the result of friction between a ring and something rough on the skin underneath. It can happen with other jewelry that fits snugly against the skin. For example, a watch or earrings could do this also.

Like invisible sandpaper, the rough material sitting on the skin rubs off tiny pieces of gold or other metals in the jewelry. The result is a dark smudge. It looks black because the pieces of gold or other metals are so small that they don’t reflect light.

The rough material can come from several sources. A common source is sunscreen that contains zinc oxide or titanium dioxide. Other examples include cosmetics, the sulfides in smog, and powders.

By and large, black dermographism is harmless. Being careful about where you apply sunscreen and cosmetics may help prevent it. You can also try gently washing your jewelry in soap and water.