Frequent diarrhea usually comes down to one of a handful of causes: a gut infection, a food your body can’t properly absorb, a medication side effect, or an underlying digestive condition. Which one applies to you depends largely on how long it’s been going on. Diarrhea lasting a few days points toward infections or something you ate, while loose stools persisting beyond four weeks suggest a chronic issue worth investigating.
Short-Term Triggers
The most common reason for a sudden bout of diarrhea is a viral infection, often norovirus or rotavirus. These spread easily through contaminated food, water, or close contact with someone who’s sick, and they typically resolve on their own within a few days. Bacterial infections from Salmonella, E. coli, Campylobacter, or Shigella can also be responsible, especially after eating undercooked meat, raw eggs, or food that’s been sitting out too long. Parasites like Giardia and Cryptosporidium are less common but tend to cause diarrhea that drags on longer than a typical stomach bug.
If your diarrhea started suddenly and came with nausea, cramping, or a low fever, an infection is the most likely explanation. Most cases clear up without treatment in two to three days.
Medications That Cause Loose Stools
Antibiotics are one of the most frequent medication-related causes. They kill off beneficial gut bacteria alongside the harmful ones, which disrupts the balance in your intestines. In some cases, this allows a bacterium called C. difficile to overgrow, leading to severe, watery, and sometimes bloody diarrhea. If your symptoms started during or shortly after a course of antibiotics, that connection is worth flagging to your doctor.
Metformin, a widely prescribed diabetes medication, is another well-known culprit. Magnesium-containing antacids can also trigger or worsen diarrhea. If you recently started a new medication or changed your dose, check whether diarrhea is listed as a side effect.
Food Intolerances and Malabsorption
Your body may be struggling to absorb certain sugars, and this is more common than most people realize. When sugars like lactose (in dairy) or fructose (in fruit, honey, and many sweetened drinks) aren’t properly absorbed in the small intestine, they pull extra water into the gut and get fermented by bacteria in the colon. The result is watery diarrhea, bloating, gas, and cramping, often within a few hours of eating the trigger food.
Celiac disease works differently but produces a similar outcome. In people with celiac, gluten (a protein in wheat, barley, and rye) triggers an immune response that damages the lining of the small intestine, impairing nutrient absorption and causing chronic loose stools. A doctor can test for lactose malabsorption with a hydrogen breath test, and celiac disease is diagnosed through blood tests and sometimes a biopsy.
One pattern to watch for: if your diarrhea improves when you skip certain foods, and it comes back when you eat them again, a food intolerance is a strong possibility.
Chronic Conditions Behind Ongoing Diarrhea
If loose stools have been your norm for more than four weeks, several conditions could be responsible.
Irritable bowel syndrome (IBS) is one of the most common causes of chronic diarrhea. It’s a functional disorder, meaning the gut looks normal on imaging and scopes but doesn’t work the way it should. IBS-related diarrhea tends to come in episodes, often triggered by stress, certain foods, or hormonal changes. Cramping that eases after a bowel movement is a hallmark.
Inflammatory bowel disease (IBD), which includes Crohn’s disease and ulcerative colitis, is a more serious possibility. Unlike IBS, IBD involves actual inflammation and damage to the intestinal lining. Symptoms often include bloody stools, weight loss, fatigue, and abdominal pain that doesn’t fully resolve after using the bathroom. Microscopic colitis, a related condition more common in older adults, causes persistent watery diarrhea without visible inflammation on standard imaging, requiring a tissue biopsy to diagnose.
What Your Stool Is Telling You
Not all loose stools are the same. On the Bristol Stool Chart, a widely used clinical tool, diarrhea falls into two categories. Type 6 is fluffy, mushy pieces with ragged edges. Type 7 is entirely liquid with no solid pieces at all. Occasional Type 6 stools aren’t necessarily a problem, but frequent Type 7 stools, especially combined with urgency, point to something more active going on in your gut.
Color matters too. Yellow or pale stools can suggest fat malabsorption. Black or tarry stools may indicate bleeding higher in the digestive tract. Bright red blood is more likely from the lower intestine or rectum. Any blood in your stool warrants a medical evaluation.
What to Eat and Drink Right Now
If you’re dealing with an acute episode, the biggest immediate risk is dehydration. You’re losing water and electrolytes with every trip to the bathroom. A simple oral rehydration solution you can make at home calls for 4 cups of water, half a teaspoon of table salt, and 2 tablespoons of sugar. Sip it steadily throughout the day rather than drinking large amounts at once.
When it comes to food, most experts no longer recommend strict restrictive diets like the old BRAT diet (bananas, rice, applesauce, toast). Once you feel up to eating, you can generally return to your normal diet. What you should avoid during an active episode includes:
- Caffeine in coffee, tea, and soft drinks
- Alcohol
- High-fat foods like fried food, pizza, and fast food
- Sugary drinks and fruit juices high in fructose
- Sugar-free gum and candies containing sugar alcohols like sorbitol
- Dairy products containing lactose, which can be harder to digest for up to a month after a diarrheal illness
That last point catches people off guard. Even if you normally tolerate dairy fine, a bout of diarrhea can temporarily reduce your ability to digest lactose. If dairy seems to make things worse during recovery, give it a few weeks.
Signs That Need Medical Attention
For adults, certain symptoms alongside diarrhea signal that it’s time to get evaluated. These include diarrhea lasting more than two days without any improvement, signs of dehydration (excessive thirst, dry mouth, dark urine, dizziness, or very little urination), severe abdominal or rectal pain, and bloody or black stools.
For children, the timeline is shorter. Diarrhea that doesn’t improve within 24 hours, a fever above 102°F, no wet diaper in three or more hours, or any sign of dehydration like sunken eyes or skin that doesn’t bounce back when pinched all call for prompt medical attention.