Nickel is a contact allergen causing Type I and Type IV hypersensitivity, mediated by reagins and allergen-specific T lymphocytes, expressing in a wide range of cutaneous eruptions following dermal or systemic exposure. As such, nickel is the most frequent cause of hypersensitivity, occupational as well as among the general population. In synoptic form, the many effects that nickel has on the organism are presented to provide a comprehensive picture of the aspects of that metal with many biologically noxious, but metallurgically indispensable characteristics. This paper reviews the epidemiology, the prognosis for occupational and non-occupational nickel allergic hypersensitivity, the types of exposure and resulting immune responses, the rate of diffusion through the skin, and immunotoxicity. Alternatives toward prevention and remediation, topical and systemic, for this pervasive and increasing form of morbidity are discussed. The merits and limitations of preventive measures in industry and private life are considered, as well as the effectiveness of topical and systemic therapy in treating nickel allergic hypersensitivity.