The literature on systemic allergic dermatitis (SAD; synonym: systemic contact dermatitis) is reviewed. Both topical drugs (from absorption through mucosae or skin) and systemic drugs (oral, parenteral, rectal) may be responsible. The topical route appears to be rare with 41 culprit topical drugs found causing SAD in 95 patients. Most reactions are caused by budesonide (especially from inhalation), bufexamac and dibucaine. SAD from systemic drugs is infrequent with 95 culprit drugs identified causing SAD in 240 patients. The drugs most frequently implicated are mitomycin C, methylprednisolone (salt, ester) and hydrocortisone (salt). The largest group of drugs consisted of corticosteroids (19%), being responsible for >30% of the reactions, of which nearly 40% were not caused by therapeutic drugs, but by drug provocation tests. The most frequent manifestations of SAD from drugs are eczematous eruptions (scattered, widespread, generalized, worsening, reactivation), maculopapular eruptions, symmetrical drug-related intertriginous and flexural exanthema (SDRIFE, baboon syndrome) and widespread erythema or erythroderma. Therapeutic systemic drugs hardly ever cause reactivation of previously positive patch tests and infrequently of previous allergic contact dermatitis. The pathophysiology of SAD has received very little attention. Explanations for the rarity of SAD are suggested. All data in this article are fully referenced (n=272).

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