Diarrhea

Diarrhea means passing loose or watery stools more frequently than is normal for the individual. It may occur suddenly and last for a short period, or it may continue or repeatedly return over several weeks. Diarrhea can appear alone or together with abdominal cramps, urgency, bloating, nausea, vomiting, fever, fatigue, or changes in appetite.

A short episode is commonly related to a viral or bacterial gastrointestinal infection, foodborne illness, travel, or a medication effect. Persistent or recurring diarrhea may require assessment for food-related digestive problems, celiac disease, irritable bowel syndrome, inflammatory bowel disease, chronic infection, medication effects, or other medical conditions.

Diarrhea is a symptom rather than a diagnosis. The likely cause depends on how suddenly it started, how long it has lasted, what the stool looks like, whether blood or mucus is present, recent travel, food exposures, medication use, associated symptoms, and the person’s general health.

How diarrhea may appear

The pattern of diarrhea can provide useful diagnostic information. Some people have only a few loose bowel movements, while others experience frequent watery stools with a strong sense of urgency. Symptoms may occur after meals, during the night, after particular foods, or without an obvious trigger.

Relevant features may include:

• loose, soft, or completely watery stool
• more frequent bowel movements than usual
• an urgent need to reach the bathroom
• abdominal pain or cramping before a bowel movement
• bloating, gas, nausea, or vomiting
• mucus, blood, or black discoloration in the stool
• stool that appears greasy, pale, or difficult to flush
• symptoms that wake the person during the night
• alternating periods of diarrhea and constipation

The number of bowel movements alone does not identify the cause. Stool appearance, duration, associated symptoms, and the effect on hydration and general condition are equally important.

Common causes of diarrhea

Viral, bacterial, and parasitic infections

Acute diarrhea is frequently caused by an infection of the digestive system. Viral gastroenteritis often causes watery diarrhea, abdominal cramps, nausea, vomiting, and sometimes fever. Bacterial foodborne illness may produce similar symptoms and can sometimes cause blood in the stool or more severe abdominal pain.

Diarrhea after international travel, untreated water, undercooked food, raw seafood, unpasteurized products, or contact with another person who has gastrointestinal symptoms may suggest an infectious cause. Some parasites can cause symptoms that persist or return over a longer period.

Several people becoming ill after eating the same food is an important detail and should be reported during the medical assessment.

Medication and antibiotic-related diarrhea

Antibiotics can disrupt the normal balance of bacteria in the intestine and cause diarrhea during treatment or in the weeks afterward. In some cases, antibiotic use can be associated with an infection caused by Clostridioides difficile, which may cause frequent diarrhea, abdominal pain, fever, or worsening general condition.

Other medications and supplements may also cause diarrhea. These can include magnesium-containing products, some diabetes medications, laxatives, certain antibiotics, cancer treatments, and other therapies. Prescribed medication should not be stopped without consulting a doctor.

Food-related digestive problems

Lactose intolerance can cause diarrhea, bloating, gas, abdominal pain, and nausea after milk or dairy products. The severity may depend on the amount of lactose consumed and the individual’s ability to digest it.

Celiac disease can cause persistent or recurring diarrhea, abdominal discomfort, bloating, fatigue, iron deficiency, weight loss, or nutrient deficiencies. Testing for celiac disease should generally be performed while the person is still consuming gluten because removing gluten beforehand can affect the results.

Other carbohydrates and food components may also cause digestive symptoms in sensitive individuals. A reproducible relationship between a specific food and diarrhea is more informative than a single isolated episode.

A food allergy differs from a food intolerance. Allergy is more likely when diarrhea or vomiting occurs rapidly with hives, itching, swelling, wheezing, or breathing difficulty. A laboratory food intolerance result should not be interpreted as proof that a particular food is causing diarrhea without considering symptoms and clinical context.

Irritable bowel syndrome

Irritable bowel syndrome can cause recurring diarrhea, abdominal pain, bloating, urgency, or alternating diarrhea and constipation. Symptoms may be influenced by meals, stress, sleep, hormonal changes, and particular foods.

Irritable bowel syndrome does not usually cause visible blood in the stool, persistent fever, or progressive unexplained weight loss. These findings require assessment for other possible causes.

Inflammatory bowel disease

Crohn’s disease and ulcerative colitis can cause persistent or recurring diarrhea, abdominal pain, blood or mucus in the stool, urgency, fatigue, fever, anemia, and weight loss. Symptoms may range from mild to severe and can fluctuate over time.

Blood and stool tests can help identify inflammation, anemia, infection, or other findings that support the need for gastroenterological evaluation. A diagnosis cannot be made from symptoms or one laboratory test alone.

Other digestive and medical causes

Chronic diarrhea may also occur with reduced absorption of nutrients, pancreatic disorders, bile acid-related problems, thyroid disease, diabetes-related digestive changes, previous abdominal surgery, or conditions that affect intestinal movement.

Diarrhea that repeatedly occurs after meals may be related to an exaggerated intestinal response, food malabsorption, infection, inflammation, or a functional digestive disorder. The timing after food does not by itself confirm food intolerance.

Symptoms that may occur with diarrhea

Associated symptoms can help determine how urgently assessment is needed and which tests may be relevant. Important symptoms include:

• abdominal pain, cramping, or marked bloating
• nausea or repeated vomiting
• fever or chills
• blood, mucus, or black stool
• dry mouth, strong thirst, reduced urination, or dizziness
• fatigue, weakness, or confusion
• unintentional weight loss or reduced appetite
• pale skin, shortness of breath, or known anemia
• skin rash, swelling, wheezing, or another rapid reaction after food
• joint pain, mouth ulcers, or other symptoms outside the digestive system

Signs of dehydration

Frequent watery stools can cause the body to lose water and electrolytes. The risk is higher when diarrhea is combined with vomiting, fever, limited fluid intake, or hot weather.

Possible signs of dehydration include:

• strong thirst and dry mouth
• dark urine or urinating less frequently
• dizziness when standing
• unusual tiredness or weakness
• sunken eyes or dry skin
• rapid heartbeat
• confusion or reduced alertness

Infants, young children, older adults, pregnant women, people with weakened immune systems, and people with chronic kidney, heart, or metabolic conditions may develop complications more quickly and should receive medical advice earlier.

When diarrhea needs medical attention

Arrange a medical assessment when diarrhea lasts longer than expected, repeatedly returns, occurs during the night, or significantly affects eating, drinking, work, sleep, or daily activities.

Medical advice is particularly important when diarrhea is accompanied by:

• blood, pus, or black stool
• persistent or severe abdominal pain
• high or ongoing fever
• repeated vomiting or inability to keep fluids down
• signs of dehydration
• unexplained weight loss
• recent antibiotic use or hospitalization
• persistent symptoms after travel
• known inflammatory bowel disease or a weakened immune system

Seek urgent medical care if diarrhea occurs with fainting, confusion, severe weakness, very little or no urine, heavy bleeding, vomiting blood, a rigid or markedly swollen abdomen, severe abdominal pain, or rapid deterioration in general condition.

How diarrhea is usually diagnosed

Medical history

The assessment usually begins with questions about when the diarrhea started, how often it occurs, stool appearance, blood or mucus, abdominal pain, fever, vomiting, recent foods, travel, contact with sick people, medication, antibiotics, and existing medical conditions.

It is also important to explain whether symptoms occur after particular foods, wake the person at night, improve after fasting, or alternate with constipation.

Clinical examination

A doctor may assess hydration, blood pressure, pulse, temperature, abdominal tenderness, swelling, bowel sounds, weight change, and other findings suggested by the symptom pattern.

Blood and stool testing

Blood tests may be used to assess anemia, inflammation, infection, electrolytes, kidney function, liver function, thyroid function, nutrient deficiencies, or signs of dehydration.

Stool testing may help identify bacteria, parasites, toxins, blood, inflammation, or other abnormalities. It may be particularly relevant when diarrhea is persistent, severe, bloody, associated with fever, follows travel or antibiotic treatment, or occurs in a person with a weakened immune system.

Depending on the symptom pattern, a gastro panel, parasite testing, Clostridioides difficile testing, inflammatory stool markers, celiac disease testing, or a broader digestive laboratory panel may be considered. No single test is appropriate for every person with diarrhea.

Additional testing

Breath testing may be considered when lactose or another carbohydrate malabsorption is suspected. Endoscopy, colonoscopy, ultrasound, or other imaging may be required when symptoms, age, examination findings, blood results, or stool tests suggest inflammation, bleeding, malabsorption, or another structural condition.

What the next step may involve

The next step depends on the duration and severity of symptoms. A short episode without warning signs may mainly require fluid and electrolyte replacement and monitoring. Persistent, recurring, bloody, or nighttime diarrhea generally requires a more structured diagnostic assessment.

Treatment may include managing dehydration, treating a confirmed infection, reviewing medication, correcting a diagnosed nutrient deficiency, managing celiac disease or another digestive condition, or using a clinically supervised dietary approach.

Antidiarrheal medicines are not suitable in every situation. They may be inappropriate when diarrhea occurs with blood in the stool, high fever, suspected invasive infection, or certain antibiotic-related infections. Medication should be selected with advice from a doctor or pharmacist.

Food intolerance testing may be considered only when symptoms show a consistent relationship with specific foods and the selected test has an appropriate clinical purpose. Broad food elimination based solely on an isolated result can lead to unnecessary restrictions and may delay investigation of another cause.

What to prepare before a medical appointment

Before an appointment or ZagrebMed inquiry, prepare information about:

• when the diarrhea started and how long it has lasted
• the approximate number of bowel movements each day
• whether the stool is watery, greasy, pale, black, bloody, or contains mucus
• associated abdominal pain, fever, vomiting, bloating, or weight loss
• signs of dehydration and the ability to drink fluids
• recent travel, unusual food, untreated water, or sick contacts
• recent antibiotics, hospitalization, or medication changes
• foods that repeatedly appear to trigger symptoms
• existing digestive conditions and previous diagnoses
• previous blood tests, stool results, imaging, or specialist reports

If diarrhea is persistent, recurring, severe, or accompanied by other digestive symptoms, you can send ZagrebMed a description of the pattern and any existing medical records. ZagrebMed can help connect the symptom with appropriate blood tests, stool testing, digestive diagnostics, or a specialist consultation in Zagreb.