Understanding Diarrhoea: Causes and Management
What is Diarrhoea?
Diarrhoea refers to the passage of loose or watery stools more frequently than your usual bowel habit. Some definitions include having three or more loose stools per day.
It can be short-term (acute diarrhoea) or long-lasting (chronic diarrhoea) if it continues for several weeks. While most cases are mild and settle on their own, persistent or severe diarrhoea may signal an underlying digestive problem that requires medical assessment.
Common Causes of Diarrhoea
Diarrhoea occurs when there is a disruption in the normal balance of digestion, absorption, and water handling throughout the gastrointestinal tract. Many organs are involved in processing what we eat and drink, so there are numerous potential causes — too many to cover fully in a short article.
Broadly, some of the common causes can be grouped by how or where the problem arises in the gut.
1. Problems with Water Absorption in the Intestines
Infections (such as viral, bacterial or parasitic gastroenteritis) can irritate the intestines and reduce its ability to absorb water.
Food intolerances, including lactose intolerance or fructose malabsorption, cause unabsorbed sugars to draw water into the bowel, resulting in watery stools.
Coeliac disease triggers an immune response that damages the small bowel lining, reducing nutrient and fluid absorption.
2. Inflammation of the Bowel Lining
Inflammatory Bowel Disease (IBD) — including Crohn’s disease and ulcerative colitis — causes chronic inflammation and ulceration, often leading to bloody diarrhoea.
Microscopic colitis is another inflammatory condition that can cause persistent watery diarrhoea, particularly in older adults.
3. Malabsorption and Digestive Enzyme Deficiencies
Pancreatic insufficiency (for example, due to chronic pancreatitis) reduces digestive enzyme production, leading to greasy, foul-smelling stools.
Bile acid malabsorption can occur after gallbladder surgery or ileal disease and often results in watery diarrhoea.
4. Functional or Motility-Related Causes
Irritable Bowel Syndrome (IBS) can cause alternating diarrhoea and constipation due to abnormal gut motility.
Thyroid disorders or post-cholecystectomy diarrhoea (after gallbladder removal) may also increase stool frequency.
5. Medication-Related or Other Causes
Certain antibiotics, magnesium-based antacids, and some chemotherapy medications can disrupt the gut microbiome or irritate the bowel, leading to diarrhoea.
Unintentional intake of foods containing sugar substitutes, such as xylitol, sorbitol, or mannitol, can also promote loose bowel actions. These are commonly found in sugar-free gum, mints, and diet products.
Diagnosis and Tests
Because there are many possible causes, your doctor will begin with a detailed history and examination to guide further testing. Depending on your symptoms, recommended investigations may include:
Stool tests – to look for infection, inflammation, or fat malabsorption
Blood tests – for coeliac disease, thyroid disorders, or nutrient deficiencies
Colonoscopy or gastroscopy – to investigate structural or inflammatory causes
Treatment Options
Treatment depends on the underlying cause. In all cases, it is important to avoid dehydration by maintaining adequate fluid intake. Good hand hygiene helps prevent the spread of infectious diarrhoea.
If weight loss or nutritional deficiency is present, your doctor may recommend a dietitian review. Other treatments may involve specific dietary adjustments, enzyme replacement, or medications prescribed by your doctor to control inflammation, infection, or motility symptoms.
This article is intended for general information only. It does not replace personalised medical advice. Please consult your doctor or gastroenterologist for assessment and guidance tailored to your situation.
Authored by Dr Walid Abu Shawish MBBS(Hons) BPharm(Hons) PGCertClinPharm FRACP.
Windsor, Melbourne Located Private Gastroenterologist & Advanced Endoscopist. For referral or contact information click here.