The normal consistency of stool and frequency of bowel movements varies in a wide range due to diet composition (e.g. rate of vegetables) and individual factors. Diarrhea is characterized by alterations away from normal behavior and is defined, alone or together, by increases of:
Water content >80%, making feces more fluid than usual
Number of bowel movements per day, e.g. from usually 1 to >3 or from usually 2 to >5
Feces weight per day, e.g. from 100 g/d to >200 g/d or from 200 g/d to >400 g/d [1,2]
Acute diarrhea (<2–4 weeks) is usually caused by bacterial, viral, or parasitic infection. In children, infection with rotavirus is the most common cause of acute diarrhea.
Chronic diarrhea (>4 weeks) is usually related to either organic disorders like the inflammatory bowel diseases (IBD) ulcerative colitis and Crohn’s disease or celiac disease or to functional disorders like the irritable bowel syndrome (IBS) .