Allergic contact hypersensitivity to metals is a delayed-type allergy. Although various metals are able to induce an allergic reaction, nickel is the most frequent cause of metal allergy worldwide. The high prevalence of skin sensitization to that metal is the result of an ubiquitous exposure, being contained in different everyday things, such as detergents, cheap jewelry, cosmetics, coins, buttons, zippers, eyeglasses, buckles, clasps, inks, dental prosthesis and foods even. However, nickel is able to induce a wide range of morphological and clinical patterns, ranging from simple allergic contact dermatitis to systemic contact dermatitis and systemic nickel allergy syndrome. The latter seems to be promoted by nickel rich-foods or through endogenous route caused by metal implants which seem to elicit mainly in loco symptoms, sometimes with catastrophic consequences as aseptic bone necrosis following the implantation of hip prosthesis.