Constant diarrhea, meaning loose stools lasting more than four weeks, usually points to an underlying condition that needs attention. It’s not just an inconvenience. Ongoing diarrhea can lead to dehydration, nutrient deficiencies, and significant disruption to daily life. The causes range from food intolerances and medication side effects to digestive disorders and hormonal imbalances.
What Counts as Chronic Diarrhea
Diarrhea that persists for more than four weeks is considered chronic. A single bad meal or stomach bug typically resolves within a few days. If you’ve had loose, watery, or mushy stools consistently for a month or longer, something beyond a temporary irritant is likely driving it.
On the Bristol Stool Scale, a visual tool doctors use to classify stool consistency, types 6 (fluffy, mushy pieces with ragged edges) and 7 (entirely liquid with no solid pieces) represent diarrhea. If most of your bowel movements fall into those categories, that’s what you’re dealing with.
Irritable Bowel Syndrome
IBS is one of the most common reasons people experience ongoing diarrhea. The diarrhea-predominant form, sometimes called IBS-D, causes frequent loose stools along with cramping, bloating, gas, and abdominal pain. Symptoms often flare after large meals or during periods of stress and may temporarily improve after a bowel movement. Some people also notice mucus in their stool.
IBS does not cause bleeding, fever, anemia, or unintentional weight loss. If you’re experiencing any of those, the problem is likely something else. IBS is a functional disorder, meaning the gut isn’t working the way it should but there’s no visible damage or inflammation in the tissue itself.
Inflammatory Bowel Disease
Inflammatory bowel disease, which includes Crohn’s disease and ulcerative colitis, causes actual inflammation and damage in the digestive tract. The key differences from IBS are the alarm symptoms: blood in the stool, unexplained weight loss, fever, and anemia. These are signs that the lining of the intestine is inflamed or ulcerated.
IBD tends to be more severe and progressive than IBS. Diarrhea from IBD can wake you up at night, which is unusual with IBS. If your chronic diarrhea comes with any of those red flags, that’s a signal to get evaluated promptly.
Food Intolerances You Might Not Know About
Many people assume they’d already know if a food was causing their symptoms. But some intolerances develop gradually or affect a surprisingly large share of the population without being diagnosed. Fructose malabsorption, for instance, is estimated to affect roughly 40 percent of people in the Western hemisphere. The intestinal cells simply can’t absorb fructose efficiently, leading to bloating, diarrhea, gas, and stomach pain after eating fruits, fruit juices, honey, or processed foods sweetened with high-fructose corn syrup.
Lactose intolerance works similarly. When your body can’t break down the sugar in dairy products, the undigested lactose draws water into the intestine and gets fermented by gut bacteria, producing gas and loose stools.
Celiac disease is another common culprit that often goes undiagnosed. In one study of patients with chronic, non-inflammatory diarrhea, 15.5 percent tested positive for celiac disease. With celiac, eating gluten triggers an immune response that damages the small intestine’s lining, impairing nutrient absorption and causing persistent diarrhea, fatigue, and weight loss. A blood test can screen for it.
Medications That Cause Chronic Loose Stools
If your diarrhea started around the time you began a new medication, the drug itself may be the cause. Nearly all medications list diarrhea as a possible side effect, but certain classes are particularly notorious:
- Antibiotics disrupt the balance of bacteria in your gut, often triggering diarrhea that can persist even after you finish the course.
- Heartburn and acid reflux drugs (proton pump inhibitors like omeprazole, as well as other acid reducers like famotidine) frequently cause loose stools with long-term use.
- Metformin, widely prescribed for type 2 diabetes, is one of the most common medication-related causes of chronic diarrhea.
- NSAIDs like ibuprofen and naproxen can irritate the gut lining and cause diarrhea, especially with regular use.
- Magnesium-containing antacids draw water into the intestine and act as a mild laxative.
- Herbal teas and supplements containing senna or other natural laxative ingredients can cause diarrhea that people don’t connect to their tea habit.
If you suspect a medication, don’t stop it on your own. Talk to the prescriber about alternatives or dose adjustments.
Bile Acid Malabsorption
Your liver produces bile acids to help digest fats. Normally, your small intestine reabsorbs most of those bile acids at the end of the digestive process. In bile acid malabsorption, that reabsorption fails. The excess bile acids spill into the colon, where they pull water into the stool and trigger urgent, watery diarrhea. Some people also experience fecal incontinence.
This condition is underdiagnosed partly because it isn’t routinely tested for. It’s particularly common after gallbladder removal and in people with Crohn’s disease affecting the end of the small intestine, but it can also happen without an obvious cause.
Small Intestinal Bacterial Overgrowth
SIBO occurs when bacteria that normally live in the large intestine colonize the small intestine in excessive numbers. These misplaced bacteria interfere with digestion in several ways. They break down bile salts before those salts can do their job of digesting fats, leading to fatty diarrhea. They ferment carbohydrates that should have been absorbed, producing gas and bloating. They can also damage the intestinal lining, further reducing your ability to absorb nutrients. The breakdown products from bacteria digesting stagnant food directly trigger diarrhea as well.
SIBO often develops alongside other conditions that slow the movement of food through the small intestine, such as diabetes, prior abdominal surgery, or certain medications. Symptoms overlap heavily with IBS, and some researchers believe a significant number of IBS cases actually involve bacterial overgrowth. A breath test can help identify it.
Thyroid Problems and Other Hormonal Causes
An overactive thyroid speeds up nearly every system in your body, including digestion. Food moves through the intestines faster than normal, which means less water gets absorbed and you end up with frequent loose stools or outright diarrhea. Other signs of hyperthyroidism include unexplained weight loss, a rapid heartbeat, anxiety, trembling hands, and heat intolerance. If your diarrhea came on alongside any of those symptoms, a simple blood test can check your thyroid function.
Patterns That Help Identify the Cause
Paying attention to when and how your diarrhea occurs can narrow down the possibilities. Symptoms that worsen after meals and improve with fasting suggest a food intolerance or malabsorption issue. Diarrhea that wakes you up at night points more toward inflammatory bowel disease or another structural problem, since IBS rarely disrupts sleep. Greasy, foul-smelling stools that float suggest fat malabsorption, which can come from SIBO, celiac disease, or pancreatic insufficiency.
Keeping a food and symptom diary for two to three weeks can reveal connections you wouldn’t otherwise notice. Note what you eat, when symptoms hit, and how severe they are. This information is genuinely useful if you end up seeing a doctor, because “I have diarrhea all the time” is a much harder starting point than “it gets worse after I eat bread and fruit, and it doesn’t wake me up at night.”
Blood in the stool, unintentional weight loss, fever, or signs of dehydration (dark urine, dizziness, extreme thirst) all warrant prompt evaluation. Chronic diarrhea on its own, even without those alarm symptoms, is worth investigating if it’s been going on for more than a month. Many of the causes are treatable once identified.