Diarrhoea in adults

Diarrhoea is a common problem in adults that occurs from time to time due to a variety of causes. The average person experiences diarrhoea about once a year. While inconvenient and sometimes unpleasant, it usually resolves on its own. Diarrhoea that lasts for more than a few days, however, may lead to dehydration and be a symptom of a more serious problem.

What is diarrhoea?

Diarrhoea is characterised by loose stools that occur three or more times a day. Watery stools occur when the bowel does not absorb enough water from wastes or when the body secretes too much water into the bowel. Alternatively, diarrhoea can be fatty if the body is having difficulty digesting fats, or ‘inflammatory’ if it contains blood and pus.

Diarrhoea is further characterized by the length of symptoms. Acute diarrhoea comes on suddenly and lasts less than two weeks, while persistent diarrhoea last two to four weeks and chronic diarrhoea continues for more than one month. Depending on the cause, additional symptoms can accompany diarrhoea, including abdominal pain and cramps, fever, bloating and nausea.

Causes of acute diarrhoea

  • Viruses, most commonly norovirus
  • Bacteria, especially Salmonella, Campylobacter, Shigella and E. coli.
  • Protozoal parasites, including Giardia
  • Medications, especially antibiotics, anticancer drugs and antacids containing magnesium
  • Food intolerance or allergies, such as lactose in milk and dairy products, fructose in fruits and sweetened beverages, and artificial sweeteners, such as sorbitol, mannitol and xylitol
  • Drinking too much alcohol
  • Feelings of anxiety

Causes of persistent diarrhoea

  • Protozoal parasites


Causes of chronic diarrhoea

  • Inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis
  • IBS (Irritable bowel syndrome)
  • Celiac disease
  • A chronic infection
  • Inability to absorb dietary fats

Who is at risk of diarrhoea?

Older individuals and people with a compromised immune system, whether from disease or certain medications, are more susceptible to diarrhoea.

Adults commonly experience traveller’s diarrhoea when they visit regions with poor sanitation and come into contact with viruses, bacteria or parasites that cause diarrhoea.

Many people experience diarrhoea while taking antibiotics. Furthermore, patients who undergo antibiotic therapy while staying in a hospital are at risk of C. difficile –associated diarrhoea, caused by the bacterium Clostridium difficile. This potentially deadly organism takes advantage of the disturbance in the gut microbiota to colonise the colon. C. difficile most frequently infects older individuals in long-term care facilities but can also cause severe infections in young, healthy people as well.

When to seek medical help

Typically, diarrhoea is short-lived in adults, lasting just a few days to a week. But if the diarrhoea has persisted for several days or is accompanied by other serious symptoms, then consult a doctor. For example, if stools are excessively watery, bloody or black, or are accompanied by persistent vomiting, a high fever or a severe or constant stomach ache, then seek medical help. Bloody diarrhoea may indicate a bacterial infection or an inflammatory condition, while black stools may be a sign of bleeding in the stomach.

Diarrhoea may lead to dehydration, which can be life-threatening in older adults and immunecompromised individuals. Seek medical help if an adult has signs of severe dehydration, such as excessive thirst, dark-coloured or no urine, fatigue or dizziness.

The role of bacteria in diarrhoea

In some cases, diarrhoea can signal that our gut bacteria are disturbed and out of balance, which is a condition called dysbiosis. This often occurs with the use of antibiotics, because they kill the good bacteria as well as the harmful ones, but can also be caused by various pathogens. Multiple studies have shown that certain probiotics can reduce the severity of diarrhoea caused by antibiotic use and from viral and bacterial infections.