There is no way for us to guarantee if a certain individual will or will not have an allergic reaction to a piece of jewelry. Individual allergies or sensitivities can come in many forms, and can even change over time for each person. Some people can wear any type of jewelry, including inexpensive base metals, with no issues, while others are irritated by almost everything, even 14k gold.
Copper
Most of us have probably experienced the phenomenon of a piece of jewelry leaving a greenish or grayish mark on our skin. It's especially common with something like a heavily-worn ring that isn't a solid precious metal, since our hands usually have the most contact with moisture, lotions, and other things.
When something leaves a green mark on the skin, it is usually because of a chemical reaction involving copper, which can be used as an alloy in jewelry metals. Sterling silver often contains copper as an alloy because pure silver is too soft to use for jewelry. Because it contains a low percentage of copper, sterling silver does not typically cause the skin to turn green. Higher percentages of copper will usually cause this issue.
Nickel
A majority of the jewelry that we carry at Dandelion does not contain nickel. Nickel is one of the most common metals to cause an allergic reaction, and many designers avoid using it in their work. That does not mean that it is never used, however! Certain metal compositions may contain nickel, and it is not always easy to determine if they do. For example, all sterling silver must be 92.5% pure silver, but the metals used as alloys (which make up the other 7.5%) can vary; copper is most commonly used, meaning the sterling silver is nickel-free, but zinc and nickel may also be included in some cases! This percentage of nickel, if it is used at all, is not enough to cause a reaction in most people, but it is not unheard of. White gold can also contain nickel (it is usually about 75% gold and 25% nickel and zinc to give it a white color).