Chronic diarrhea is defined as loose or watery stools, lasting longer than four weeks and affects approximately 6 to 7% of adults in the US.
Chronic diarrhea is typically defined as the passage of loose or watery stools (Bristol Stool Scale types 5–7) with a frequency of ≥3 per day, lasting more than 4 weeks. It affects 1–5% of adults and has a broad differential diagnosis.
Chronic diarrhea is diarrhea that lasts 4 weeks or longerand usually means loose or frequent stools that keep happening rather than a short-lived stomach bug.
It’s important to get evaluated if diarrhea is ongoing, because it can lead to dehydration, electrolyte problems, weight loss, and malnutrition.
Classification by Stool Characteristics
Watery diarrhea (most common): Secretory (e.g., microscopic colitis, bile acid malabsorption, medications, endocrine causes), osmotic (e.g., lactose intolerance, magnesium-containing antacids), or functional (e.g., IBS-D).
Fatty/malabsorptive (steatorrhea; greasy, foul-smelling, floating stools): Celiac disease, pancreatic exocrine insufficiency (EPI), small intestinal bacterial overgrowth (SIBO), giardiasis.
Inflammatory (with blood, mucus, or leukocytes): IBD (Crohn’s, ulcerative colitis), infectious colitis, ischemic colitis, radiation colitis.
Common Causes of chronic diarrhea:
Functional: IBS with diarrhea (IBS-D), functional diarrhea (often after ruling out organic causes).
Malabsorption/Maldigestion: Celiac disease, lactose/fructose intolerance, EPI (e.g., from chronic pancreatitis), SIBO.
Inflammatory: Microscopic colitis (lymphocytic or collagenous—common in older adults, especially women on NSAIDs/PPIs), IBD.
Infectious: Persistent parasites (Giardia, Cryptosporidium), especially in immunocompromised or travelers; rarely chronic bacterial.
Medications: Metformin, antibiotics, PPIs, NSAIDs, chemotherapy, laxatives (factitious).
Other: Bile acid diarrhea (post-cholecystectomy or ileal disease), hyperthyroidism, diabetes (autonomic neuropathy), post-surgical (e.g., gastric bypass), microscopic colitis, alcohol, or dietary factors.
Red Flags Onset after age 50 Unintentional weight loss Nocturnal diarrhea Visible blood or melena Iron-deficiency anemia Family history of IBD, celiac, or colorectal cancer Severe dehydration or systemic symptoms
More than 90% of patients with chronic diarrhea have a non-infectious etiology.
Functional diarrhea is a condition in which more than 25 percent of bowel movements in the preceding three months are loose or watery, but it is not associated with significant abdominal pain.
Chronic diarrhea due to a small bowel source, such as celiac disease or small, intestinal, bacterial overgrowth, is typically associated with large volume diarrhea and weight loss, with or without steatorrhea.
Celiac disease is an autoimmune condition defined by enteropathy, precipitated by exposure to gluten in the diet in genetically predisposed individuals, and small intestinal, bacterial overgrowth is characterized by excessive bacteria in the small bowel.
Chronic diarrhea due to colon pathology includes bile acid diarrhea, and microscopic colitis, typically presenting with frequent, low volume stools, with or without urgency and excess mucus.
Bile acid diarrhea is characterized by excess bile acids in the colon and microscopic colitis is characterized by chronic inflammation oncolon biopsies, despite normal endoscopic appearance.
Pathophysiology: Oral fluid intake of 2-3 L per day and fluid secretion of 7–8 liters per day by salary glands, the stomach, pancreas, liver, and small intestine accounting for the fluid in the gastrointestinal tract.
Physiologically the small intestine reabsorbs approximately 7 to 9 liters per day and the colon reabsorbs approximately 1.5 L per day, leaving 100 to 200 mL of fluid per day, which is normally excreted in the stool.
Evaluation:
Evaluation of chronic diarrhea includes serological testing for celiac disease with a tissue transglutaminase immunoglobulin A level, along with total immunoglobulin, a evaluation, and stool testing for fecal calprotectin to evaluate for inflammatory bowel disease.
Patients with G.I. bleeding, unexplained weight loss, 45 years or older, nocturnal diarrhea, steatorrhes, and/or iron deficiency anemia should undergo colonoscopy to evaluate for colorectal cancer as well as upper endoscopy.
During colonoscopy, random biopsies are recommended to evaluate from microscopic colitis that affect 13% of patients with chronic diarrhea.
If evaluation does not identify a cause of chronic diarrhea, the likely diagnoses are IBS-D or functional diarrhea and lifestyle modification, regularly scheduled meals, exercise, 8 cups of non-caffeinated fluids/day,, limiting caffeine to 3 cups of fewer daily, and avoiding alcohol and carbonated beverages.
Initial Evaluation
History & Physical: Onset, pattern, triggers-diet, meds, travel, surgery, associated symptoms (pain relieved by defecation suggests IBS), weight changes, incontinence.
Basic Labs: CBC (anemia), CMP (electrolytes, renal function), CRP or ESR, celiac serology (tTG-IgA + total IgA), TSH, fecal calprotectin or lactoferrin to screen for inflammation.
Stool Studies: Occult blood, calprotectin/lactoferrin Giardia antigen (or multiplex PCR panel) Fecal fat if malabsorption suspected C. difficile toxin if risk factors
Colonoscopy with random biopsies (especially for microscopic colitis) Upper endoscopy/duodenal biopsy (celiac)
Breath testing (lactose, SIBO)
Imaging or specific tests (e.g., for bile acid malabsorption, pancreatic imaging/enzymes)
A stepwise approach can achieve a diagnosis in >90% of cases.
In suspected IBS-D without alarms, limited testing (celiac, calprotectin, Giardia) is often sufficient per AGA guidelines.
Management of chronic diarrhea:
Supportive: Hydration, electrolytes, soluble fiber (e.g., psyllium), dietary modification (low-FODMAP trial if IBS suspected, avoid triggers).
Treatment: general treatment of chronic diarrhea, includes dietary modifications, such as consuming a diet low in fermentable oligosaccharides (legumes, wheat, onions, garlic), disaccharides (lactose), and monosaccharides (fructose), and poly polyols (suborbital, mannitol, or medications, such as opiate agonists, anticholinergics, or 5- hydroxytryptamine 3 antagonists can be prescribed.
Symptomatic: Loperamide (first-line antimotility, safe for chronic use in non-infectious cases). Other options: bile acid sequestrants (cholestyramine for bile acid diarrhea), antidiarrheals.
Targeted: Treat underlying cause (e.g., gluten-free diet for celiac, enzymes for exocrine pancreatic insufficiency, budesonide for microscopic colitis, rifaximin for SIBO/IBS-D).
Lifestyle: Smaller meals, stress management, probiotics in select cases.
Chronic diarrhea significantly impacts quality of life—many patients respond well to targeted therapy once the cause is identified.
The pattern can help narrow the cause: watery diarrhea often suggests functional, medication-related, or secretory causes, while fatty or greasy stools suggest malabsorption.
Abdominal cramping, bloating, urgency, nausea, and unintended weight loss are also common accompanying symptoms.