Systemic contact dermatitis.

Systemic contact dermatitis (SCD) describes a cutaneous eruption in response to systemic exposure to an allergen. The exact pathologic mechanism remains uncertain. The broad spectrum of presentations that are often nonspecific can make it difficult for the clinician to suspect this disease, but it is an important diagnosis to consider in cases of recalcitrant, widespread, or recurrent dermatitis, in which patch testing often reveals allergy to nickel or balsam of Peru. Diagnosis and appropriate management can be life-altering for affected patients. This article on SCD provides an overview of the disease with descriptions of common allergens and some insight into the possible mechanism of action seen in SCD.