Systemic contact dermatitis to hydroxyzine.

Systemic contact dermatitis is an underreported type of delayed hypersensitivity caused by a systemically administered substance. When interpreting patch test reactions, it is important to obtain a history of all current related oral medications. Many oral medications can cross-react with structurally similar topical antigens and induce systemic contact dermatitis. Identification and elimination of the inciting agent can lead to resolution of otherwise chronic, unresponsive eczema. We report a case of systemic contact dermatitis to hydroxyzine in a patient who was patch tested positive to ethylenediamine. Repeated oral provocation with hydroxyzine reproduced her eczema on several occasions. We conclude that systemic contact dermatitis to hydroxyzine, a common medication used to treat pruritus, must be considered as a potential cause for unresponsive eczema.