Oral or parenteral exposure to certain contact allergens may elicit an eczematous skin reaction in sensitized individuals. This phenomenon has been called systemic contact dermatitis (SCD) and is relatively rare when compared with classical contact dermatitis. We reviewed and analysed the clinical and immunologic features of 42 patients with SCD caused by ingestion of Rhus (Toxicodendron), 24 males and 18 females, average age 44 years (range 24–72). Several of such patients (33%) had a known history of allergy to lacquer. The patients developed skin lesions such as generalized maculopapular eruptions (50%), erythroderma (29%), vesiculobullous lesions (14%) and erythema multiform (EM)‐like lesions (7%). Many patients (57%) developed leucocytosis with neutrophilia (74%). In some patients (5%), abnormalities of liver function developed. We also analysed lymphocyte subsets in the peripheral blood of 12 patients. The lymphocyte subsets studied were T cells (CD3), B cells (CD19), natural killer (NK) cells (CD3–CD16+/CD56+), helper/inducer cells (CD4), cytotoxic/suppressor cells (CD8) and helper/suppressor ratio (CD4/CD8). The lymphocyte subsets of all 12 patients studied were within the normal range. Moreover, there were no differences between patients with a history of allergy to lacquer and those without a history of allergy to lacquer. Therefore, rather than an immunologic response, the skin eruption seems to be caused by a toxic reaction because of Rhus.