What are possible causes of persistent diarrhea?

Persistent or chronic diarrhea, defined as diarrhea lasting longer than four weeks, can be caused by medical conditions such as irritable bowel syndrome, inflammatory bowel diseases, chronic pancreatitis, food allergies and parasitic infections, notes UpToDate.com.

Inflammatory bowel diseases such as ulcerative colitis, celiac disease and Chron's disease are commonly linked to persistent diarrhea. Chronic pancreatitis resulting from injury to the pancreas can lead to chronic diarrhea, claims the American College of Gastroenterology. Individuals who suffer from lactose, sorbitol or fructose intolerance are also at increased risk for chronic diarrhea if their diet is not altered to eliminate the offending substance. Lastly, certain parasitic infections of the intestine, such as giardiasis, can cause chronic diarrhea if left untreated.