Skin reactions to jewelry are most commonly caused by a nickel allergy.
It's a chemical reaction. Sometimes after wearing jewelry, your skin that was in contact will turn green. It's because the jewelry wasn't in fact silver or gold, but cheap copper.
Jewelry changing color can happen because of different reasons. Chemicals, lotions, chlorine in water, all of these can change the color of some metals like white gold. If your skin is changing colors you may be having a reaction to one of the alloys in the metal your wearing. See if this reaction happens with all metals that you wear to try to pin point your allergic reaction.
If it is low carat gold (10 or so), the alloy metals might react to your skin. Anything but 24k will have some alloy in it, and jewelry is rarely made of 24k, since it is so soft. If you are highly sensitive to the alloys, even a small amount might cause a reaction. Furthermore, you sure your jewelry is really solid gold, and not plated? Plated jewelry will often react with the skin as you have described.
Jewelry that is uncomfortable or jewelry that you make have an allergic reaction to should not be worn.
http://www.helium.com/items/597008-why-do-some-jewelry-metals-turn-skin-green
It is best to by hypo-allergenic metal body jewelry for sensitive skin.
Stop wearing costume jewelry.
Yes
I think it is bad for skin
The only thing that is not a chemical reaction is the hot glue gun melting the glue. A copper bowl tarnishing, a spoiling peach, and jewelry turning your skin green are all chemical reactions.
Copper is what is in jewelry that turns skin green after lengthily wear. If the aluminum is If the aluminum is anodized it won't corrode at all.
I had a reaction to salicylic acid where it burnt my skin, i suggest moisturizing cream and cortaid cream to soothe your skin and heal it.