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what causes sickness and diarrhoea

Sickness and diarrhoea usually happen when something irritates or infects your stomach and intestines, making your body try to get rid of it quickly.

Main medical causes

  • Infections (most common)
    • Viruses: norovirus, rotavirus, adenovirus and others can inflame the gut and cause sudden vomiting and diarrhoea (“stomach bug” or viral gastroenteritis).
* Bacteria: E. coli, Salmonella, Campylobacter, Vibrio cholerae and others from undercooked food, unsafe water or poor hygiene can trigger severe diarrhoea, sometimes with fever or blood.

* Parasites: Giardia and similar organisms from contaminated water or food can cause longer‑lasting diarrhoea, weight loss and tiredness.
  • Food‑related triggers
    • Food poisoning: toxins or germs in spoiled or undercooked food cause sudden nausea, vomiting and diarrhoea a few hours to a day after eating.
* Food intolerance: trouble digesting certain sugars (like lactose or sucrose) or sweeteners (sugar alcohols) can lead to bloating, gas and diarrhoea after eating them.

* Food allergies: some people’s immune systems react to certain foods, irritating the gut and causing diarrhoea among other symptoms.
  • Medicines and substances
    • Antibiotics, some antidepressants, chemotherapy drugs, magnesium‑containing products and laxatives can upset the balance in your intestines and cause diarrhoea.
* Alcohol, overeating and some herbal supplements may irritate the stomach and bowel, leading to nausea, cramping and loose stools.
  • Chronic gut conditions
    • Irritable bowel syndrome (IBS), Crohn’s disease, ulcerative colitis and celiac disease can cause ongoing or recurrent diarrhoea, pain and bloating.
* Problems with the pancreas or small intestinal bacterial overgrowth can interfere with digestion and cause chronic diarrhoea and weight loss.
  • Other body‑wide causes
    • Systemic infections (including COVID‑19) and some cancers can produce diarrhoea and sickness as part of a broader illness.
* Strong emotions and stress can trigger gut nerves and speed things up, sometimes causing nausea, diarrhoea or both.

How the body reacts

When your gut senses germs, toxins or something it cannot digest properly, the lining becomes inflamed and secretes more fluid, and the muscles speed up movement, so food and waste rush through before the body can absorb water, causing loose or watery stools. Vomiting often happens at the same time because the upper digestive tract also tries to force out whatever is causing harm.

Common real‑life scenarios

  • “Stomach flu” going around school or work: usually a viral infection spread by close contact, contaminated hands or surfaces.
  • Getting sick on holiday: “traveller’s diarrhoea” from local water, raw foods or street food contaminated with bacteria or parasites.
  • Sudden diarrhoea after milk or ice cream: possibly lactose intolerance, especially if it happens repeatedly.
  • Loose stools after antibiotics: disruption of normal gut bacteria or infection with C. difficile, which especially affects people after antibiotic courses or hospital stays.

When it’s dangerous

You should seek urgent medical help if there is any of the following:

  • Signs of dehydration (very dry mouth, dizziness, passing little or no urine, extreme tiredness).
  • Blood in the stool, black/tarry stool or very severe abdominal pain.
  • High fever, confusion or symptoms lasting more than a few days (especially in children, older adults or those with long‑term illness).

Latest and “trending” angles

  • Public health agencies regularly warn about norovirus and other diarrhoeal outbreaks, especially in colder months and in places like care homes, schools and cruise ships.
  • Globally, unsafe water, poor sanitation and hygiene remain major drivers of diarrhoeal disease, particularly in low‑resource settings, and are a key focus for international health organisations.

Simple prevention tips

  • Wash hands with soap and water before eating and after using the toilet or changing nappies.
  • Drink safe, treated water; be cautious with ice, salads and raw foods when travelling.
  • Cook meat, eggs and seafood thoroughly and avoid unpasteurised milk.
  • Keep kitchen surfaces and utensils clean to prevent cross‑contamination.

Information gathered from public forums or data available on the internet and portrayed here.