30th July 2026

Background

Erythema Multiforme (EM) is an immune-mediated hypersensitivity reaction affecting cutaneous and mucosal membranes. The condition is characterised by typical targetoid lesions with concentric rings that develop in a symmetrical acral distribution with mucosal involvement in a small number of patients. The majority of cases are triggered by herpes simplex virus (HSV), but other triggers exist including drugs and vaccinations. It is self-limiting but has a tendency to recur in 30% of affected patients. Although historically believed to be part of the same disease process that causes Steven-Johnsons Syndrome(SJS)/Toxic Epidermal Necrolysis (TEN) , emerging research has provided evidence to suggest EM is its own disease entity.