Allergic contact dermatitis is a T-cell dependent, delayed-type (Type IV) hypersensitivity reaction that has a high impact both in terms of patient morbidity and economics. This type of hypersensitivity reaction is primarily instigated by small lipophilic chemicals (haptens) with a molecular weight less than 500 Daltons. These chemical allergens trigger a complex immunologic cascade in the skin, which leads to the clinical picture of nickel allergic contact dermatitis. Skin reactions most often occur at the site of nickel contact, but is recognized to cause systemic reactions, also known as systemic contact dermatitis (SCD). In addition to contact to a nickel-containing item, the object must have a sufficient amount of nickel to be released in order to be absorbed by the skin to induce an allergic reaction.

Nickel allergic contact dermatitis can present as a localized or systemic reaction. One subset of SCD is systemic nickel allergy syndrome (SNAS). While the pathophysiology is highly complex and not fully elucidated, it can present with an array of skin, respiratory, and gastrointestinal manifestations. In addition, one study found 1% of patients that are sensitized to nickel.