Nickel is the most common cause of contact allergy in general population and the most frequently detected allergen in patients patch tested for suspected allergic contact dermatitis (ACD). Nickel Allergy: ACD from nickel is a typical type IV hypersensitivity. Nickel allergy is mostly caused by non-occupational 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 an 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 a systemic contact dermatitis. Patch testing represents the gold standard for diagnosis of ACD from nickel. Treatment includes avoidance of contact with products containing nickel and the patient’s education about 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 summarize epidemiology, pathomechanism, clinical patterns, treatment and prevention programs.

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