STERLING SILVER, BRONZE, AND BRASS ALL OXIDIZE DUE TO MOISTURE IN THE AIR, CHEMICALS THEY ARE EXPOSED TO, AND EVEN CERTAIN SKIN TYPES. METALS THAT MAKE UP THE ALLOY ARE REACTING TO WHAT THEY ARE EXPOSED TO. JEWELRY IS NOT INDESTRUCTIBLE. HERE'S A FEW WAYS TO KEEP IT LOOKING IT'S BEST THE LONGEST. 

Always remove your jewelry before swimming, bathing, cleaning, working out, or while doing any laborious activities.  When not being worn, it is best to store jewelry in a separate bag, pouch, or box away from any excess moisture, such as the bathroom. Avoid sleeping in your jewelry. Do not bend cuffs or bracelets to take on and off everyday, frequent bending or firm squeezing will weaken the metal and cause cracks. Metal can be very gently adjusted once to find the perfect fit. Once adjusted, the opening should be just wide enough to slip on and off over the hand (or sideways on the narrowest part of the wrist), but not too wide so that it falls off easily. When you treat your jewelry with care, you will get many, many years of wear and enjoyment out of it. 

All brass and bronze has a higher copper content in the alloy that can be reactive to certain skin types and most definitely, to moisture. The common reaction to this is skin turning "green" or slightly darker. This is a natural reaction in the metal alloy and is harmless. If you notice this happening (especially with rings) you can choose to paint a layer of clear nail polish on the piece where it touches skin.