When natural yellow gold is mixed with alloys to strengthen it to it's 10 or 14 karat composition, it can often take in metals like nickel which can cause an allergy for those with sensitive skin. Our experience in the industry helped us create nickel free versions for couples with a known allergy to nickel. While Nickel is the most common allergy inducing metal, it's important to consult a physician to determine what metals you are sensitive to.