Erythema multiforme is an immunological skin reaction with reddened, slightly raised cockade-like blotches emerging especially in the extremities. A vesicle may develop in the centre, and the blotches may grow bigger and merge to form map-like areas. The triggering factor often is an infection, such as the activation of a herpes virus, or some drug. The rash may be recurrent. A disorder confined to a small area does not need treatment, but for a more wide-spread form a corticosteroid either orally or topically may be indicated. If the symptoms rapidly increase in severity and abrasions develop on the mucosal membranes, the patient should be referred to a hospital.