Quick answer: The most common causes of watery diarrhoea are infections (viruses, bacteria, parasites), food intolerances, certain medicines, and chronic bowel conditions such as IBS or microscopic colitis. Most acute cases resolve on their own within a few days, but persistent symptoms require assessment by a specialist.
If you pass loose or completely liquid, watery stools more than three times a day, this is referred to as watery diarrhoea. This unpleasant condition affects almost everyone at some point in their lives, and although it is often harmless, it can occasionally be a sign of a more serious illness. Below, we explain in simple terms what can cause watery diarrhoea, when you should see a doctor, and how Endomedix’s team of experts can help clarify the underlying causes of your symptoms.
What counts as watery diarrhoea?
According to the medical definition, diarrhoea is characterised by mushy or liquid stools occurring at least three times a day. This corresponds to categories 6 and 7 on the Bristol Stool Scale (a system for classifying stool consistency): grade 6 refers to mushy, loose stools, whilst grade 7 refers to completely liquid, watery stools containing no solid matter.
We distinguish between three groups based on duration:
- Acute diarrhoea: It lasts for up to 14 days and is usually caused by an infection.
- Prolonged diarrhoea: It lasts between 14 and 30 days.
- Chronic diarrhoea: It lasts longer than 30 days and requires a more thorough investigation.
What mechanisms underlie watery diarrhoea?
There may be several physiological processes underlying the development of watery diarrhoea. Understanding these helps us to understand why individual symptoms can vary so much.
Osmotic diarrhoea
Osmotic diarrhoea occurs when substances that are not absorbed in the intestine draw water into the intestinal lumen. It is characterised by the fact that it stops when one fasts. Causes include carbohydrate malabsorption, lactose intolerance, the consumption of artificial sweeteners (such as sorbitol), and certain laxatives.
Secretory diarrhoea
In cases of secretory diarrhoea, the intestinal wall secretes increased amounts of fluid, or water reabsorption is reduced. This type occurs regardless of meals and does not stop even when fasting. It may be caused by alcohol, caffeine, antibiotics, certain hormone-producing tumours, or microscopic colitis.
Inflammatory diarrhoea
Inflammatory diarrhoea is caused by damage to the lining of the bowel. In such cases, blood and white blood cells may be present in the stools, often accompanied by fever, abdominal pain and weight loss. Typical causes include inflammatory bowel diseases (Crohn’s disease, ulcerative colitis), infections and ischaemic colitis.
Peristaltic disorder (motility-related diarrhoea)
In this case, bowel movements are accelerated, meaning that stools do not spend enough time in the large bowel for water to be absorbed. The most common cause is irritable bowel syndrome (IBS), but hyperthyroidism and amyloidosis can also cause it.
The most common causes of watery diarrhoea
Causes of infectious origin
Acute watery diarrhoea is most commonly caused by an infection. Pathogens can enter the body in a number of ways, typically through contaminated food or water.
Viral infections:
- Rotavirus: It causes severe, watery diarrhoea, particularly in young children, accompanied by fever and vomiting.
- Norovirus (Norwalk virus): It is accompanied by nausea, abdominal cramps and a fever, and usually lasts for 12–72 hours.
- Adenovirus and astrovirus: They can also cause watery diarrhoea.
Bacterial infections:
- Salmonella: watery diarrhoea accompanied by a fever and abdominal pain.
- Enterotoxigenic E. coli (ETEC): the most common cause of traveller’s diarrhoea, characterised by watery stools and cramps.
- Campylobacter: one of the most common types of bacterial diarrhoea, which may also be accompanied by blood.
- Clostridium difficile: It typically develops following a course of antibiotics and is the most common cause of hospital-acquired diarrhoea.
Parasites:
- Giardia lamblia and amoeba can also cause persistent, watery diarrhoea.
Food intolerances and malabsorption disorders
Nutrients that are not properly absorbed can lead to osmotic diarrhoea. The most common underlying conditions are:
- Lactose intolerance: A lack of the enzyme that breaks down lactose leads to bloating, abdominal pain and diarrhoea.
- Coeliac disease (celiac disease): It is characterised by persistent diarrhoea, bloating and weight loss following the consumption of gluten.
- Fructose and sorbitol intolerance: These sugars and sweeteners are poorly absorbed and may cause diarrhoea.
Side effects of medicines
A number of medicines can cause watery diarrhoea. The most common include antibiotics, magnesium-containing antacids, certain cytostatic drugs and non-steroidal anti-inflammatory drugs.
Chronic bowel diseases
Persistent watery diarrhoea is often caused by an underlying chronic condition:
- Irritable bowel syndrome (IBS): The diarrhoea-predominant form (IBS-D) causes loose stools, abdominal pain and bloating, which may be exacerbated by eating or stress.
- Microscopic colitis: It causes unexplained, persistent watery diarrhoea, often in women over the age of 60. It is characterised by an urgent need to pass stools and night-time bowel movements. A histological sample taken during a colonoscopy is required for diagnosis, as the intestinal mucosa appears almost completely intact to the naked eye.
- Inflammatory bowel diseases (IBD): Crohn’s disease and ulcerative colitis can also cause persistent diarrhoea.
When should you see a doctor?
Most cases of acute diarrhoea clear up on their own within a few days. However, if you experience certain warning (so-called „alarm”) symptoms, you should definitely consult a specialist:
- bloody or black stools
- A fever of over 38.5 °C lasting for more than 48 hours
- more than six bowel movements a day
- signs of severe fluid loss (dizziness, weakness, reduced urine output)
- unexplained weight loss
- symptoms lasting longer than 30 days
- Age 70 or over, or a weakened immune system
These symptoms may indicate that the complaint is caused by a more serious underlying condition, which requires targeted investigation.
How is watery diarrhoea investigated?
Several types of tests may be required to identify the cause of persistent or recurrent diarrhoea. The following options are available at Endomedix’s gastroenterology centres:
- Laboratory tests: blood tests, inflammatory markers, thyroid function and coeliac disease screening.
- Stool analysis: to detect pathogens, parasites and signs of inflammation.
- Hydrogen breath test: to confirm lactose intolerance or bacterial overgrowth.
- Endoscopic examinations: A colonoscopy allows for a detailed examination of the inside of the bowel, as well as the taking of tissue samples to rule out microscopic colitis and inflammatory bowel diseases.
This examination is particularly important because, for example, microscopic colitis can only be diagnosed by taking a tissue sample, as the intestinal mucosa appears normal to the naked eye.
Endomedix’s expertise in gastroenterology
From Endomedix At our gastroenterology centres, experienced specialists investigate the causes of digestive complaints, including watery diarrhoea. During the consultation, our doctors will review your symptoms, medical history and lifestyle in detail, and then draw up a personalised examination plan.
If the investigation of the symptoms requires a colonoscopy, at Endomedix COLONOSCOPY UNDER ANAESTHESIA We carry out the procedure as part of this programme. It is important to emphasise that, for professional reasons, at Endomedix we use general anaesthesia exclusively, rather than sedation – this ensures that the examination is completely pain-free and that the patient can undergo the procedure in a calm and safe state. The general anaesthesia is supervised by an experienced anaesthetist, who monitors the patient’s vital signs throughout the procedure.
If you experience persistent or recurrent watery diarrhoea, do not delay seeking medical advice. Book an appointment for a gastroenterology consultation at Endomedix, where our specialist doctors will help you understand the causes of your symptoms and find the right solution.
Frequently asked questions
How long does acute watery diarrhoea last?
Acute watery diarrhoea, usually caused by an infection, generally clears up on its own within a few days, or up to 14 days at the most. If the symptoms persist beyond this or are accompanied by warning signs, it is advisable to consult a specialist.
What should you do at home if you have watery diarrhoea?
The most important thing is to ensure adequate fluid replacement, as diarrhoea leads to significant loss of water and electrolytes. It is recommended to drink oral rehydration solutions. However, if symptoms persist, or if you have a fever or blood in your stools, you should seek medical attention.
When does watery diarrhoea indicate a more serious illness?
It may be a sign of a more serious condition if diarrhoea lasts for more than 30 days, if there is blood in the stools, if it is accompanied by unexplained weight loss, or if a high, persistent fever develops. In such cases, a specialist gastroenterological examination is recommended.
What tests can be used to determine the cause of watery diarrhoea?
To identify the cause, laboratory and stool tests, a hydrogen breath test and, if necessary, a colonoscopy are required. During a colonoscopy, a tissue sample is also taken, which is essential, for example, for the diagnosis of microscopic colitis.
Can stress cause watery diarrhoea?
Yes. In the case of irritable bowel syndrome (IBS), both stress and eating can trigger or exacerbate watery diarrhoea. This symptom is linked to a disturbance in peristalsis, that is, accelerated bowel movements.
