Nickel is the most common cause of contact allergy in the general population and the most
frequently detected allergen in patients patch tested for suspected allergic contact dermatitis (ACD).
ACD from nickel is a typical type IV hypersensitivity. Nickel allergy is mostly caused by nonoccupational
exposure, such as jewelry and clothing decorations, metal tools, medical devices (mainly
orthopedic and orthodontic implants, cardiovascular prosthesis), eyeglasses, utensils, keys, pigment for
paint, cosmetics, and food (mainly legumes, chocolate, salmon, peanuts). Occupational exposure can
involve several workers (mechanics, metalworkers, platers, hairdressers, jewelers, workers in the constructions
and electronic industries), classically involving hands and forearms. The classic clinical
pattern of ACD caused by nickel is characterized by eczematous dermatitis involving the sites of direct
contact with the metal. Non-eczematous-patterns are reported, including lichenoid dermatitis, granuloma
annulare, vitiligo-like lesions, dyshidrosiform dermatitis, and vasculitis. In the case of systemic
exposure to nickel, sensitized patients could develop systemic contact dermatitis. Patch testing represents
the gold standard for the diagnosis of ACD from nickel. Treatment includes avoidance of contact
with products containing nickel and the patient’s education about the possible use of alternative products.
A recent EU nickel directive, regulating the content and release of nickel from products, has
caused a decrease of nickel contact allergy in some European countries. Nickel allergy is a relevant
issue of public health with significant personal, social, and economic impact. This review summarizes
epidemiology, pathomechanism, clinical patterns, treatment, and prevention programs.