EM aetiology is unknown but it is thought to be a hypersensitivity reaction triggered by multiple factors. Some of these include reactions to drugs and viral infections, often HSV(found in 70% of cases).

It causes skin lesions that have a distinct appearance known as target lesions. It affects women more than men.  EM affects the oral mucosa causing

• Desquamative gingivitis
• Ulcerative lesions on the cheeks and lips
• In some forms, the lesions may have a thick crusty layer

Further info and images here on a JCDA EM case study.