 Crohn disease can affect any part of gastrointestinal tract, from mouth to anus.When it involves the mouth alone, some authors refer to this as "oral Crohn disease", distinguishing it from OFG, and others suggest that OFG is the same condition as Crohn disease when it presents in the oral cavity.OFG may represent a delayed hypersensitivity reaction, but the causative antigen(s) is not identified or varies form one individual to the next.