Erythema multiforme is a hypersensitivity disorder in response to infections and medications. It is usually seen in adults and children.
It is characterized by symmetric red, patchy lesions especially on the arms and legs.
The disorder caused in response to Herpes simplex virus is believed to involve an immunological component and so this is considered as the autoimmune part of the disorder. This, however, lacks clarity as the hypersensitivity is initiated even in the presence of Mycoplasma pneumonia
Medications such as sildenafil, hydantoins, barbiturates, penicillins, sulfonamides and phenothiazines are other causes of erythema multiforme.
This disorder is of immunologic origin but is not autoimmune in nature.