Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Erythema multiforme ?
    ### Response:
    Erythema multiforme (EM) refers to a group of hypersensitivity disorders characterized by symmetric red, patchy lesions, primarily on the arms and legs. The cause is unknown, but EM frequently occurs in association with herpes simplex virus, suggesting an immunologic process initiated by the virus.
    