You are having an allergy to the metal to be precise used in the necklace (likely nickel). You need to stop wearing it. This is the singular way to fic the rash. You can also use a hydrocortisone cream to relieve clear it up faster. You can buy it at the pharmacy. Good luck.
I have the same point when I wear any metal but gold. If you take the necklace rotten and leave it off for awhile the impulsive will go away.
it sounds like you are allergic to it - or one of it's components,
lots of culture are allergic to nickel, a few people can only wear 24 K gold ingots.
fixing it - wash with peaceable soap, moisturize. it will probably vanish overnight, if you quit wearing the necklace.
most of us just own sensitive skin. And people with sensitive cant wear cheap necklaces. so ever time you obtain breakout on the back of your neck use some Aveeno. To give a hand.
You're probably allergic to the nickle in the metal. Try Claire's or Icing. They carry nickle free jewelry.
Answers: Sometimes jewelry that is more costume-ish (or cheapy stuff like clairs) is silver, or gold ingots dipped but nickle underneath...a lot ppl are sensitive to nickel based jewelry and can not wear it (you are probably one of those kind of ppl) stop wearing the jewelry wash your neck beside warm soap and water and consequently apply a anti-itch cream (like cortizone) to the area...it should calm down within a day or two.