Chronic Diarrhea: Causes and What to Do

What counts as chronic diarrhea

Doctors define diarrhea by stool consistency more than frequency: stools that are loose or watery (type 6 or 7 on the Bristol stool chart). It is acute if it lasts less than 2 weeks, persistent at 2 to 4 weeks, and chronic beyond 4 weeks. Chronic diarrhea affects roughly 1 in 20 adults at any time.

Chronic diarrhea is often grouped by stool type, which points to the cause:

Common causes of chronic diarrhea

Functional and dietary causes

• Irritable bowel syndrome (IBS-D): diarrhea with belly pain that eases after a bowel movement, bloating and urgency, often triggered by stress or certain foods. There is no blood, weight loss or night-time diarrhea.
• Lactose intolerance: bloating, gas and loose stools after dairy.
• Fructose and sugar alcohols: sorbitol, mannitol and xylitol in sugar-free gum and sweets, and large amounts of fruit juice.
• Caffeine and alcohol, especially regular heavy drinking.

Bowel diseases

• Celiac disease: an immune reaction to gluten that damages the small intestine. It can cause diarrhea, bloating, weight loss, anemia and fatigue, or very subtle symptoms. Testing must be done while you are still eating gluten.
• Inflammatory bowel disease: Crohn's disease and ulcerative colitis cause diarrhea, often with blood, urgency, pain and weight loss.
• Microscopic colitis: watery, non-bloody diarrhea, mainly in people over 50 and more often women. The bowel looks normal on colonoscopy, so biopsies are needed. It is linked to NSAIDs, PPIs and SSRIs.
• Bile acid diarrhea: bile acids reaching the colon cause watery diarrhea. It is common after gallbladder removal or ileal surgery and is often mistaken for IBS.
• Small intestinal bacterial overgrowth (SIBO): bloating and loose stools, often after bowel surgery or with diabetes.
• Colorectal cancer: a change in bowel habit, blood in the stool and anemia, especially after 50.

Medicines

Many medicines cause diarrhea: metformin, magnesium-containing antacids and supplements, antibiotics, some blood pressure medicines, PPIs, SSRIs, NSAIDs, colchicine and chemotherapy. Laxative overuse is an often overlooked cause.

Infections

Most infections are short-lived, but some persist: giardia (after drinking untreated water or travel), C. difficile after antibiotics, and parasites in travelers. People with HIV or weakened immunity can have chronic infections.

Other medical causes

• Pancreatic insufficiency from chronic pancreatitis or cystic fibrosis, causing fatty stools
• Overactive thyroid
• Diabetes, through nerve damage to the gut, SIBO or metformin
• Previous surgery, including gallbladder removal, bowel resection and weight-loss surgery
• Rare hormone-secreting tumors (carcinoid, VIPoma)

How doctors investigate chronic diarrhea

Questions

Expect questions about stool appearance, frequency, night-time symptoms, blood, weight change, diet, alcohol, travel, recent antibiotics, medicines, surgery and family history of bowel disease or cancer. A stool diary for 1 to 2 weeks is helpful.

First-line tests

• Blood tests: blood count (anemia), iron, B12, folate, kidney and liver function, thyroid, CRP and celiac antibodies (tTG-IgA)
• Stool tests: infection (including giardia and C. difficile), fecal calprotectin (a marker of bowel inflammation that helps tell IBD from IBS), and sometimes fecal elastase for pancreatic function
• Fecal immunochemical test (FIT) for hidden blood in some settings

Further tests

• Colonoscopy with biopsies for red flags, raised calprotectin, or suspected microscopic colitis
• Upper endoscopy with duodenal biopsy to confirm celiac disease
• SeHCAT scan or blood tests for bile acid diarrhea where available
• Breath tests for lactose intolerance or SIBO
• CT or MRI of the abdomen in selected cases

Treatment

Treat the cause

• Gluten-free diet for celiac disease
• Anti-inflammatory and immune medicines for IBD and microscopic colitis
• Bile acid binders for bile acid diarrhea
• Pancreatic enzyme supplements for pancreatic insufficiency
• Antibiotics for giardia, C. difficile or SIBO
• Stopping or switching a culprit medicine

Managing symptoms

• Low-FODMAP diet under a dietitian's guidance helps many people with IBS.
• Soluble fiber such as psyllium can firm up stools.
• Loperamide slows the bowel and reduces urgency. Follow the label dose. Do not use it with bloody diarrhea or fever unless a doctor advises it.
• Fluids: drink enough to keep urine pale. Oral rehydration solutions replace salts when diarrhea is heavy.

Protecting your skin

Frequent loose stools irritate the skin around the anus. Clean gently with water, pat dry, and use a barrier cream.

Frequently asked questions

When is diarrhea considered chronic?

Diarrhea is considered chronic when loose or watery stools continue for 4 weeks or longer. Diarrhea lasting 2 to 4 weeks is called persistent. Any diarrhea lasting more than a few weeks should be discussed with a doctor, even if you feel otherwise well.

What is the most common cause of chronic diarrhea?

In developed countries, irritable bowel syndrome with diarrhea is the most common cause. Other frequent causes are food intolerances, medicines, bile acid diarrhea, celiac disease, microscopic colitis and inflammatory bowel disease. Tests are needed to tell them apart.

Can stress cause chronic diarrhea?

Stress does not cause bowel disease, but it strongly affects gut function and is a common trigger for IBS flares. Stress-related diarrhea should not include blood, weight loss or night-time symptoms. Those features suggest another cause and need investigation.

Is chronic diarrhea a sign of cancer?

Occasionally. Bowel cancer can change bowel habits, often with blood in the stool, anemia or weight loss, mainly in people over 50. Most chronic diarrhea is not cancer, but persistent changes, especially with red flags, should be checked with a FIT test or colonoscopy.

What should I eat if I have chronic diarrhea?

It depends on the cause. Limit caffeine, alcohol, sugar alcohols and very fatty meals. Try reducing dairy for 2 weeks to see if lactose is a trigger. Do not cut out gluten before celiac testing. A dietitian can guide a low-FODMAP trial if IBS is diagnosed.