Jewellery made of some metals (copper being one of them) can react with the moisture and naturally occurring acids on your skin causing a temporary yukky green mark. Stress, skin type, soaps and lotions, body temperature can all cause changes in your skin so each person will have a different experience to the next. If you have had this problem with jewellery before it’s likely to happen with any jewellery containing copper (including sterling silver which contains a percentage of copper too).
To combat this reaction I coat all copper elements in my jewellery with either wax or acrylic lacquer which provides a barrier between your skin and the metal. Keeping your jewellery dry and clean will also help avoid the dreaded green mark.