Diarrhoea is one of the most common digestive problems people face worldwide, affecting millions every year and ranging from a brief inconvenience to a serious health threat. Understanding what causes loose, watery stools and knowing how to respond can help you protect yourself and your family from complications.

How Common Is Diarrhoea Around the World?

Diarrhoea remains a major health challenge globally, particularly for young children. The World Health Organization reports that diarrhoeal disease is the third leading cause of death in children aged 1 to 59 months. Each year, approximately 443,832 children under five years old die from diarrhoea, with an additional 50,851 deaths occurring in children aged 5 to 9 years.^[1]

The scale of the problem extends beyond mortality. Globally, there are nearly 1.7 billion cases of childhood diarrhoeal disease every year.^[1] In developed countries like the United States, research suggests that people experience acute diarrhoea about once a year on average, though the actual number may be higher since many people don’t seek medical care for this condition.^[2] Children tend to experience it more frequently, with an average of twice per year.^[9]

The burden of diarrhoeal illness varies significantly by region and economic development. In developing countries, contaminated food and water supplies contribute heavily to the problem. Meanwhile, in developed nations, technological progress and mass food production have paradoxically contributed to the persistence of foodborne illness despite higher food production standards.^[13] An estimated 48 million foodborne diarrhoeal illnesses occur annually in the United States alone, resulting in more than 128,000 hospitalizations and 3,000 deaths.^[13]

What Causes Diarrhoea?

Diarrhoea develops when your digestive system cannot properly process food and liquids. Normally, food and fluids pass from your stomach into your small intestine, where nutrients and most fluid are absorbed. The remaining waste and some water then pass into your large intestine, where more water is absorbed before waste is eliminated. When the cells in your intestines become irritated, this normal process speeds up, and your body cannot absorb enough fluid, resulting in loose or watery stools.^[4]

The most common cause of diarrhoea is a virus that infects your gut, a condition often called gastroenteritis or the “stomach flu.” In adults, the norovirus is the most frequent culprit, while rotavirus is the most common cause of acute diarrhoea in children.^[9] These viral infections spread easily from person to person or through contaminated surfaces.

Bacterial infections also frequently cause diarrhoea. You can ingest harmful bacteria from contaminated food or water, leading to what many people call food poisoning. Common bacteria responsible for diarrhoeal illness include certain strains of Escherichia coli, Salmonella, Campylobacter, and Shigella.^[5] When traveling to areas with poor sanitation, people often develop “traveler’s diarrhoea” from exposure to unfamiliar bacteria in food or water.^[9]

Parasites represent another infectious cause, though less common than viruses and bacteria. Organisms like Giardia and Cryptosporidium can contaminate water supplies, particularly in mountainous regions or areas with inadequate water treatment. These parasitic infections can cause diarrhoea that develops one to four weeks after exposure.^[8]

Beyond infections, many other factors can trigger diarrhoea. Medications are a frequent cause, with antibiotics being particularly problematic. While antibiotics kill harmful bacteria causing illness, they also destroy helpful bacteria in your gut, leading to an imbalance that can result in diarrhoea. Other medications that commonly cause diarrhoea include antacids containing magnesium, certain cancer drugs and treatments, and overuse of laxatives.^[9]

Food intolerances and sensitivities can also lead to diarrhoea. If you’re lactose intolerant, your body struggles to digest lactose, the sugar found in dairy products, resulting in loose stools. Some people have difficulty digesting fructose, a sugar in honey and fruits that’s also added as a sweetener to many foods. People with celiac disease experience diarrhoea because their bodies cannot properly break down gluten, a protein found in wheat, barley, and rye.^[9]

Who Is at Higher Risk?

While anyone can develop diarrhoea, certain groups face greater risk. Children who are malnourished or have weakened immune systems are most vulnerable to life-threatening diarrhoea. People living with HIV also face significantly higher risk of severe diarrhoeal disease.^[1]

Your daily activities and environment can increase exposure to diarrhoea-causing agents. People who work in hospitals, nursing homes, or daycare facilities have greater contact with infectious diseases. Those who travel frequently, particularly to countries with limited sanitation, face higher risk of exposure to contaminated water and food.^[2]

If you have been exposed to untreated water, such as while camping or hiking, your risk of parasitic infections increases. Food allergies or existing digestive tract problems also make diarrhoea more likely. Additionally, taking certain medicines like antibiotics or cancer treatments puts you at elevated risk.^[2]

Older adults and people with weakened immune systems require special attention, as they are more susceptible to dehydration and complications from diarrhoea. Pregnant women also need to be cautious, as diarrhoea can affect both mother and baby if it leads to dehydration or malnutrition.^[2]

Recognizing the Symptoms

Diarrhoea is defined as passing three or more loose or liquid stools per day, or more frequent bowel movements than what is normal for you. The term specifically refers to the consistency of stool rather than just frequency. Frequent passing of formed stools is not diarrhoea, nor is the passing of loose, pasty stools by breastfed babies, which is normal.^[1]

Beyond the characteristic watery stools, diarrhoea often comes with other uncomfortable symptoms. You may experience cramping or pain in your abdomen, along with bloating and an urgent need to use the restroom. Many people also feel nausea, and in some cases, vomiting occurs alongside the diarrhoea. Loss of appetite and general fatigue are common, as your body works to fight off whatever is causing the problem.^[3]

The severity of diarrhoea can vary considerably. Mild diarrhoea means having only a few loose, watery stools in a day. Moderate diarrhoea involves many loose stools throughout the day, but not more than ten times. Severe diarrhoea is characterized by more than ten watery stools within 24 hours, which can quickly lead to dehydration if fluids are not replaced.^[8]

Dehydration represents one of the most serious complications of diarrhoea. Your body loses water and essential electrolytes (minerals like sodium and potassium) with each loose stool. Signs of dehydration include a dry and sticky mouth, producing no urine for six hours, no tears when crying, and sunken eyes. In children, parents should also watch for unusual drowsiness or unresponsiveness.^[6]

Different Types of Diarrhoea

Healthcare providers classify diarrhoea based on how long it lasts. Acute diarrhoea is the most common type, lasting less than one week to two weeks. This is typically the result of a viral or bacterial infection and usually resolves on its own without treatment.^[2]

Persistent diarrhoea lasts between two and four weeks. While still considered a short-term problem, persistent diarrhoea warrants closer attention, especially if it doesn’t show signs of improvement or if other symptoms develop.^[2]

Chronic diarrhoea continues for at least four weeks or comes and goes repeatedly over a long period. This type may indicate a more serious underlying condition such as inflammatory bowel disease (including Crohn’s disease or ulcerative colitis), irritable bowel syndrome, food intolerances, or malabsorption problems. Research suggests that up to 5% of people in the United States experience chronic diarrhoea.^[2]

Diarrhoea can also be classified by its underlying mechanism. Watery diarrhoea can be secretory (where the intestine secretes too much fluid), osmotic (where certain substances prevent water absorption), or functional (related to conditions like irritable bowel syndrome). Fatty diarrhoea occurs when your body cannot properly digest or absorb fats, often appearing greasy or oily. Inflammatory diarrhoea involves damage to the intestinal lining and may contain blood or mucus, warranting immediate medical evaluation.^[7]

Preventing Diarrhoea

Many cases of diarrhoea can be prevented through simple hygiene and lifestyle measures. The single most effective prevention strategy is proper hand washing. Washing your hands thoroughly with soap and clean water, especially before eating or preparing food and after using the toilet, dramatically reduces the spread of infectious agents that cause diarrhoea.^[1]

Access to safe drinking water is fundamental to preventing diarrhoeal disease. A significant proportion of diarrhoea worldwide can be prevented through safe drinking water and adequate sanitation and hygiene. If you’re uncertain about water quality, especially when traveling or camping, use bottled water, boil water before drinking, or use appropriate water purification methods.^[1]

Food safety plays a crucial role in prevention. Always ensure that food is properly cooked, especially meat, poultry, and eggs. Avoid eating raw or undercooked foods in areas where food safety standards may be questionable. Wash fruits and vegetables thoroughly before eating. Store food at appropriate temperatures and avoid leaving perishable items at room temperature for extended periods.^[13]

For parents, vaccinations offer important protection for children. Rotavirus vaccines have proven highly effective at preventing severe diarrhoea in young children. Following recommended vaccination schedules helps protect your child from this common and potentially dangerous cause of diarrhoea.^[1]

When traveling to areas with poor sanitation, take extra precautions. Stick to bottled or boiled water, avoid ice cubes made from tap water, and be cautious about eating raw vegetables or fruits you haven’t peeled yourself. Street food, while tempting, may pose higher risk in areas with limited hygiene standards. Some travelers carry antibiotics prescribed by their doctor for use if traveler’s diarrhoea develops.^[13]

If you’re taking antibiotics, consuming foods rich in beneficial bacteria, such as yogurt with live cultures, may help maintain a healthy balance of gut bacteria and reduce the risk of antibiotic-associated diarrhoea. However, always consult with your healthcare provider before taking probiotics alongside antibiotics.^[5]

Understanding What Happens in Your Body

To understand diarrhoea, it helps to know how your digestive system normally works. Your digestive tract is a complex system designed to extract nutrients from food while maintaining careful control over fluid balance. When you eat, food travels through your esophagus to your stomach, where it’s partially broken down by stomach acid. From there, it moves into your small intestine, where most nutrients and water are absorbed into your bloodstream.^[4]

The remaining material then enters your large intestine, also called the colon. Here, more water is removed from the waste material, and the contents become more solid. Normally, this process results in formed stools that retain some moisture but are not liquid. The timing of this entire process is carefully regulated by your body to maintain proper hydration and eliminate waste efficiently.^[4]

When diarrhoea occurs, this delicate balance is disrupted. In infectious diarrhoea, viruses, bacteria, or parasites invade the cells lining your intestinal tract, causing inflammation and irritation. This irritation triggers several changes in how your intestines function. The infected or inflamed cells may secrete additional fluid into the intestinal contents rather than absorbing it. At the same time, the irritation causes your intestines to contract more frequently and forcefully, pushing contents through faster than normal.^[1]

Because everything moves through your system too quickly, your large intestine doesn’t have enough time to absorb water from the waste material. The result is stool that contains much more liquid than usual. Essential salts and minerals that would normally be absorbed also pass through your system, which is why diarrhoea can lead to electrolyte imbalances.^[4]

In the past, severe dehydration and fluid loss were the main causes of diarrhoea-associated deaths. Today, while dehydration remains a serious concern, other complications such as septic bacterial infections (where bacteria enter the bloodstream) are increasingly recognized as important causes of severe illness and death from diarrhoea, particularly in children who are malnourished or have weakened immune systems.^[1]

Different causes of diarrhoea affect the body through distinct mechanisms. When you have a food intolerance, such as lactose intolerance, your body lacks the enzymes needed to break down certain food components. These undigested substances then draw water into your intestine through a process called osmosis, leading to watery stool. With inflammatory bowel diseases, chronic inflammation damages the intestinal lining, impairing its ability to absorb nutrients and water while also causing it to secrete additional fluid.^[5]

Some medications cause diarrhoea by altering the normal bacterial population in your gut. Your intestines are home to trillions of beneficial bacteria that help with digestion and protect against harmful organisms. When antibiotics kill these helpful bacteria along with the infection they’re treating, the resulting imbalance can allow harmful bacteria to multiply or can simply leave your digestive system unable to function normally, resulting in loose stools.^[9]

Understanding these underlying processes helps explain why treatment approaches vary depending on the cause. Addressing dehydration is important regardless of the cause, but treating the underlying problem—whether it’s an infection, inflammation, or food intolerance—requires different strategies tailored to the specific mechanism causing your symptoms.^[11]