Loose stools lasting more than a few days usually point to something your body is reacting to, whether that’s a food, a medication, or an underlying digestive condition. Once it crosses the four-week mark, it’s considered chronic diarrhea, and that’s the threshold where identifying the cause becomes important rather than just waiting it out. The good news is that most causes are treatable once pinpointed.
What Counts as Chronic Diarrhea
Doctors define chronic diarrhea as predominantly loose stools lasting longer than four weeks. On the Bristol Stool Scale, a visual guide used in clinical settings, types 5 through 7 fall into diarrhea territory: soft blobs with clear edges, fluffy or mushy pieces with ragged edges, or fully liquid stool with no solid pieces at all. If you’ve been seeing types 6 or 7 for weeks, that’s not just an upset stomach lingering. Something is actively disrupting your digestion.
Dietary Causes That Are Easy to Miss
Before assuming the worst, it’s worth looking at what you’ve been eating and drinking. Some of the most common triggers hide in everyday products. Sugar alcohols like sorbitol, mannitol, and xylitol, found in sugar-free gum, candy, protein bars, and even some medications, pull extra water into your intestines. If you’ve recently increased your intake of these products, they could easily explain weeks of loose stools.
Lactose intolerance is another frequent culprit, and it can develop or worsen in adulthood even if dairy never bothered you before. The same goes for fructose, found in high amounts in certain fruits, honey, and high-fructose corn syrup. Large amounts of caffeine or alcohol can also speed up your gut enough to prevent stools from firming up. If you’ve changed your diet in the past month or two, that’s the first place to investigate.
Medications That Cause Persistent Loose Stools
Several common prescription medications list diarrhea as a side effect, and it doesn’t always start immediately. Metformin, one of the most widely prescribed diabetes drugs, is well known for causing ongoing stomach problems including chronic loose stools. Antibiotics can disrupt gut bacteria for weeks after you finish a course. Proton pump inhibitors (heartburn medications), magnesium supplements, and certain blood pressure drugs can also keep your stools soft indefinitely. If your loose stools started around the time you began or changed a medication, that connection is worth raising with your prescriber.
IBS: The Most Common Functional Cause
Irritable bowel syndrome is one of the most frequent explanations for ongoing stool changes without an obvious trigger. It’s classified as a syndrome, meaning it’s defined by a pattern of symptoms rather than visible damage to the intestines. A colonoscopy in someone with IBS looks completely normal.
The hallmark pattern is abdominal pain or discomfort that improves after a bowel movement, along with changes in how often you go or what your stool looks like. Some people with IBS alternate between diarrhea and constipation. Others deal mostly with loose stools. Symptoms tend to flare after large meals or during periods of stress. Bloating, gas, mucus in the stool, and a feeling of incomplete evacuation are all common. IBS doesn’t cause weight loss, bleeding, or fever. If you’re experiencing those, something else is going on.
Inflammatory Bowel Disease
Unlike IBS, inflammatory bowel disease (Crohn’s disease and ulcerative colitis) involves actual inflammation and damage to the intestinal lining that shows up on imaging and biopsies. The key differences from IBS are the presence of systemic symptoms: unintended weight loss, blood in the stool, anemia, fever, and fatigue that goes beyond just feeling tired from disrupted sleep. IBD can cause destructive inflammation and permanent harm to the intestines if left untreated, which is why these warning signs matter.
Bile Acid Malabsorption
Your liver produces bile acids to help digest fat. Normally, your small intestine reabsorbs most of them. When that process fails, excess bile acids spill into the colon, irritating its lining and triggering it to secrete extra fluid. The result is frequent, urgent, watery diarrhea with cramping. Some people also notice greasy or fatty-looking stools that are hard to flush. Bile acid malabsorption is thought to be underdiagnosed because its symptoms overlap heavily with IBS, and it often responds well to specific treatment once identified.
Microscopic Colitis
This condition causes chronic watery diarrhea, belly pain, bloating, and sometimes weight loss or trouble controlling bowel movements. What makes it tricky is that the colon looks normal during a colonoscopy. The inflammation is only visible under a microscope when tissue samples are examined, which is how it gets its name. Microscopic colitis is most common in people over 50 and affects women more often than men. Smoking increases the risk, particularly in younger adults. Some research also suggests a link with post-menopausal hormone therapy.
Signs That Need Prompt Attention
Certain symptoms alongside chronic loose stools signal that you should talk to a doctor sooner rather than later:
- Black, tarry stools or visible blood or pus in your stool
- Unintended weight loss you can’t explain through diet changes
- Fever that accompanies your digestive symptoms
- Severe abdominal or rectal pain
- Signs of dehydration like dark urine, dizziness, or dry mouth
- Six or more loose stools per day
- Irritability or lack of energy beyond normal fatigue
People who are pregnant, over 65, currently on antibiotics, or have a weakened immune system are more likely to develop complications from prolonged diarrhea and should be in closer contact with their doctor throughout.
How the Cause Gets Identified
If your loose stools have lasted four weeks or more, a doctor will typically start with blood work and a stool test. Blood tests check your blood count, electrolyte levels, and kidney function to gauge how the diarrhea is affecting your body. Stool tests look for bacterial or parasitic infections that can sometimes linger for weeks without obvious signs like fever.
If those come back normal, the next step often depends on your symptoms. A hydrogen breath test can identify lactose intolerance: you drink a lactose-containing liquid, and your breath is measured at intervals for hydrogen, which rises when lactose isn’t being properly absorbed. For suspected inflammatory conditions or microscopic colitis, a colonoscopy or flexible sigmoidoscopy allows a doctor to visually inspect the colon and take small tissue samples. An upper endoscopy examines the stomach and upper small intestine when malabsorption is suspected.
None of these tests are particularly painful, though the colonoscopy prep (clearing out your bowels beforehand) is the part most people find unpleasant. The process of identifying the cause can take a few weeks between appointments and results, but narrowing it down is what makes targeted treatment possible rather than just managing symptoms indefinitely.
Simple Steps While You Sort It Out
While you’re working toward a diagnosis, a few practical adjustments can help. Keep a food diary for one to two weeks, noting what you eat and when your symptoms are worst. This is one of the fastest ways to spot a dietary trigger you might be overlooking. Cut back on sugar-free products, caffeine, and alcohol temporarily to see if that shifts anything. Stay on top of hydration, because weeks of loose stools quietly deplete fluids and electrolytes even if you don’t feel dramatically dehydrated. Water is fine, but adding something with electrolytes (broth, an oral rehydration drink, or coconut water) helps more than water alone.
Soluble fiber from foods like oats, bananas, and white rice can help firm up stools in the short term. Insoluble fiber from raw vegetables and whole grains can make things worse when your gut is already irritated, so easing off those temporarily is reasonable. Probiotics may help in some cases, particularly after antibiotic use, though the evidence varies depending on the underlying cause.