An infection may be involved. There appears to be a genetic susceptibility and environmental factors may be involved. Patients who smoke tend to have more active Crohn's disease. Crohn's disease affect the gastrointestinal tract from the mouth to the anus. It is characterized by inflammation of the bowel wall, which becomes chronic to the extent that fibrosis or scarring occurs.
Diarrhea is the most common complaint.
Stools can be very loose or partly formed, with or without blood. Patients may have abdominal pain which is due to inflammation, cramping, infection or even obstruction. On account of significant diarrhea, patients may have weight loss and dehydration. Onset in childhood may cause growth retardation. Some patients may present with obscure fevers.