Your poop is diarrhea because your intestines are moving waste through too quickly, not absorbing enough water along the way. Normally, your large intestine pulls water back into your body as digested food passes through. When something disrupts that process, whether an infection, a food your body can’t handle, stress, or medication, the result is loose, mushy, or fully liquid stool. The cause depends on how long it’s been happening and what else is going on in your life.
What Counts as Diarrhea
Not every soft stool qualifies. On the Bristol Stool Scale, a tool doctors use to classify stool consistency, diarrhea falls into two categories: fluffy, mushy pieces with ragged edges (type 6) or completely watery liquid with no solid pieces at all (type 7). These happen when your bowels move too fast and too often, pushing waste out before your intestines have time to absorb water from it.
Timing matters too. Diarrhea that lasts 2 days to 2 weeks is considered acute, and it’s usually caused by something temporary like a stomach bug. If it stretches to 2 to 4 weeks, it’s classified as persistent. Anything beyond 4 weeks is chronic diarrhea, which points to an underlying condition that needs attention.
Infections Are the Most Common Cause
If your diarrhea came on suddenly, an infection is the most likely explanation. Viruses cause the majority of acute diarrhea cases. Norovirus, rotavirus, and adenoviruses are the primary culprits, and they typically resolve on their own with rest and fluids. You’ve probably picked one up from contaminated food, a sick person, or a shared surface.
Bacterial infections are less common but tend to hit harder. Salmonella, Campylobacter, E. coli, and Shigella can all cause severe diarrhea, sometimes with blood or mucus. These bacteria produce toxins that actively force your intestinal lining to pump water into your gut rather than absorb it. This type of diarrhea doesn’t stop even if you skip meals, because the problem isn’t what you’re eating. It’s the toxin driving your cells to secrete fluid. Bacterial diarrhea sometimes needs treatment, especially if you develop a fever, see blood in your stool, or can’t stay hydrated.
Food Your Body Can’t Process
Some diarrhea happens because undigested substances pull water into your intestines. This is called osmotic diarrhea, and it stops when you stop eating the trigger food. Lactose intolerance is a classic example. If your body doesn’t make enough of the enzyme that breaks down the sugar in dairy, that undigested lactose draws water into your gut. Symptoms usually start within a few hours of eating or drinking dairy products.
Sugar alcohols, the sweeteners found in sugar-free gum, protein bars, and diet candies, work the same way. Your body can’t fully absorb them, so they sit in your intestines and attract water. Sorbitol is especially potent: it can trigger a laxative effect at surprisingly small amounts, roughly 12 grams for a 150-pound man. That’s the equivalent of a few sticks of sugar-free gum or a handful of sugar-free mints. Erythritol is better tolerated, requiring about three to four times as much to cause the same effect.
Fructose, found naturally in fruit and added to many processed foods as high-fructose corn syrup, causes the same problem for people who absorb it poorly. Caffeine and alcohol both speed up gut motility, which can tip borderline stools into diarrhea territory.
Medications That Cause Diarrhea
If your diarrhea started around the same time as a new medication, the drug may be responsible. Antibiotics are one of the most common offenders. They kill off beneficial gut bacteria along with the harmful ones, disrupting the microbial balance your intestines rely on for normal digestion. This can cause diarrhea during a course of antibiotics or even in the weeks after finishing one.
Metformin, a widely prescribed diabetes medication, frequently causes loose stools, especially when first starting it. Magnesium-containing antacids work as osmotic agents in the gut, pulling in water the same way undigested sugars do. If you’re taking any of these and dealing with persistent diarrhea, it’s worth discussing alternatives or timing adjustments with whoever prescribed them.
Stress and Anxiety
Your brain and your gut are in constant communication, and stress can directly change how your intestines behave. When you’re anxious or under pressure, your brain releases a stress hormone that acts on receptors throughout your digestive tract. In the colon specifically, this hormone increases motility, meaning your intestines contract faster and push contents through before water can be properly absorbed. That’s why you might get diarrhea before a big presentation, during a stressful week at work, or in the middle of a personal crisis.
This isn’t imagined or psychosomatic in the dismissive sense. The stress response physically changes how fast your colon moves. People with irritable bowel syndrome (IBS) are especially sensitive to this effect, which is why stress is one of the most reliable IBS flare triggers.
Chronic Conditions to Consider
If your diarrhea has been going on for more than four weeks, something deeper may be driving it. IBS with diarrhea is one of the most common explanations, characterized by recurring episodes of loose stool often linked to certain foods, stress, or hormonal cycles. Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis cause ongoing inflammation in the digestive tract that leads to chronic diarrhea, sometimes with blood.
Celiac disease, an autoimmune reaction to gluten, damages the lining of the small intestine and interferes with nutrient absorption. Hyperthyroidism speeds up your metabolism across the board, including gut transit time. Less commonly, certain hormone-producing tumors can force the intestinal lining into a state of constant fluid secretion.
Staying Hydrated While It Lasts
The main risk with diarrhea isn’t the diarrhea itself. It’s the water and electrolytes you’re losing. Plain water alone doesn’t replace the sodium and potassium that leave with each watery stool. Oral rehydration solutions work because they contain a specific balance of sodium and glucose that triggers your intestines to actively absorb fluid. The ideal ratio is roughly 60 milliequivalents per liter of sodium paired with 80 to 110 millimoles of glucose. You can buy premade solutions at any pharmacy, or make a rough version with water, salt, and a small amount of sugar.
For acute diarrhea from a virus or mild food poisoning, the goal is to keep drinking, eat bland foods as tolerated, and wait it out. Most episodes resolve within a few days without any specific treatment.
Signs That Need Attention
Most diarrhea is harmless and short-lived, but certain patterns warrant a closer look. Blood or black tar-like color in your stool, a fever above 102°F, signs of dehydration like dark urine or dizziness, and diarrhea that persists beyond two weeks all suggest something beyond a routine stomach bug. Unintentional weight loss alongside chronic diarrhea is particularly significant, as it can indicate malabsorption or inflammatory disease. Diarrhea that wakes you from sleep is also notable, since functional conditions like IBS rarely cause nighttime symptoms.