Nickel Allergy is an adverse immune response of the body when exposed to nickel products. Nickel is a silver-colored metal found naturally in the environment and is usually mixed with other metals to produce various items like coins and jewelry. The immune system naturally fights off harmful substance to defend the body. In this case, the immune system take Nickel mistakenly into virus or anything dangerous. In result, the immune system starts to produce chemicals that eventually triggers allergic reaction.