Silver and bronze (alloy of copper and tin – nickel free) are metals that over time can oxidize and become more dark. Other factors that can contribute to the dulling of metal are skin sweat (do not use in pools and spas) and, in general, contact with all corrosive substances (special attention to the use of disinfectants).
Depending on the pH value of your skin, these metals can cause the appearance of a halo on the skin that disappears with washing. Unfortunately, this reaction is very subjective but should not be considered an allergic reaction.

Some tips for their cleaning:

If the jewelry has lost its luster you can use a specific product for bronze or silver or rub the jewel with a solution of water and bicarbonate to pass with a microfiber cloth or an old toothbrush. Dry thoroughly and return the jewelry to its packaging. Air is the worst enemy of oxidation.

Careful with stones:

You should always put on your jewelry as the last thing. Make-up, perfumes and various products should be applied before wearing your jewelry, as these products can ruin the stones.