Systemically induced (hematogenous) contact eczema.

The oral or parenteral application of certain contact allergens may elicit eczematous skin reactions "from the inside" in sensitized individuals; this phenomenon has been called "systemically induced eczema" or "hematogenous contact eczema". Both the clinical morphology and dermatopathology are very similar to classical allergic contact eczema. The distribution of skin lesions is mostly symmetrical and may affect the face or the anogenital area. The pathophysiology involves T-lymphocytes and probably secretion of cytokines similar to the well-known phenomenon of "flare-up". The most important contact allergens known to elicit systemically induced contact eczema are metal salts, drugs, phytoallergens and balsam of Peru. After careful diagnosis, a specific allergen avoidance is the basis of prophylaxis and therapy.