Diarrhoea: causes, symptoms and treatment explained

Everyone’s bowel habits are different both in terms of how often stools are passed and their consistency. Diarrhoea broadly refers to passing stools more often than usual and stools that are looser than what is normal for you. 

Stools passed during diarrhoea are medically classed as type 6 or type 7 stools on the Bristol stool chart. Type 6 stools are mushy (semi-liquid) and comprise fluffy pieces with ragged edges, while type 7 stools are completely liquid with no formed pieces.

Here, we will explore the most common causes of diarrhoea, when to see a doctor and how to treat diarrhoea, as well as how diarrhoea affects children.

Common causes of diarrhoea

Diarrhoea can be acute, which means it usually gets better within a week, or chronic (long-term), which means it lasts for several weeks or more. 

Acute diarrhoea is usually caused by a viral infection (eg norovirus, rotavirus and adenovirus), bacterial infection (eg Escherichia coli or Clostridium difficile) or a toxin present in something you have eaten or drunk. Toxins that cause diarrhoea are usually produced by bacteria in foods or drinks or, in the case of shellfish, by algae. 

Chronic diarrhoea occurs when not enough fluid in your stools is absorbed out of your colon into your bloodstream. This can be caused by certain medications, such as antibiotics, which can disrupt the balance of healthy bacteria in your gut. Other medications that can cause diarrhoea include antacids, antidepressants, proton pump inhibitors and chemotherapy. 

Other causes of chronic diarrhoea include food intolerances and medical conditions, such as:

• Bowel cancer  
• Coeliac disease
• Inflammatory bowel disease (ie Crohn’s disease and ulcerative colitis)
• Small intestinal bacterial overgrowth (SIBO)
• Whipple disease

When to see a doctor

If you have acute diarrhoea and you can identify the cause (eg food poisoning or a viral infection), you may not need to see a doctor. However, it is important to stay hydrated and avoid contact with other people to stop the spread of any infectious agent (eg a virus or bacteria) that’s causing your diarrhoea.

If a vulnerable individual has diarrhoea that lasts more than 6 days or they have become seriously unwell, it is important to see a GP. This is because diarrhoea can lead to severe dehydration, which can cause kidney damage. 

Vulnerable individuals include children, older people and those with heart conditions, diabetes and poor kidney function. Signs that they may be seriously unwell include: 

• A fever
• Bloody stools
• Confusion
• Dizziness
• Feeling weak and/or drowsy
• Severe abdominal pain

The amount of urine they pass may also reduce and their blood pressure may drop (hypotension).

If you have chronic diarrhoea for which a cause has not already been identified, you should see your GP to have this investigated. 

Diagnosing the cause of diarrhoea

If you have acute diarrhoea that has lasted more than 6 days or is making you seriously unwell, your doctor will ask for a stool sample so they can test it for bacteria and viruses that cause diarrhoea. 

If you have chronic diarrhoea, your doctor will also ask for a stool sample and may test for protein that is increased during inflammation of the bowel called calprotectin. This can suggest the presence of inflammatory bowel disease. 

If these investigations rule out inflammatory bowel disease and depending on any other symptoms and your medical history, your doctor may recommend dietary changes to manage your diarrhoea. 

If your doctor suspects that you have non-inflammatory bowel disease, they may recommend that you have a colonoscopy to reach a diagnosis. This involves having a thin, flexible, telescope-like device with a light and a camera on the end (colonoscope) inserted via your back passage (rectum) to examine your colon. 

Diarrhoea in children

The most common cause of diarrhoea in children is viral gastroenteritis. This is an infection of the gut that can be caused by several different viruses. It is most commonly caused by norovirus, adenovirus and rotavirus. However, cases of rotavirus infection in children in the UK have reduced since 2013 due to the introduction of rotavirus vaccination for all newborns. 

Children may also develop diarrhoea due to food poisoning. This occurs when they eat food that is infected with bacteria such as Escherichia coli, Salmonella or Campylobacter. 

In children, diarrhoea often causes vomiting. It can also cause abdominal pain that eases after a bout of diarrhoea, headaches, a fever and body aches. 

Most cases of diarrhoea in children will resolve within 6 days; however, their stools may take another week or so to return to a normal consistency. They may also temporarily develop an intolerance to lactose — the sugar found in dairy products — until the balance of healthy bacteria in their gut recovers. 

While they have diarrhoea, it is important to keep them well-hydrated and replace lost salts (electrolytes). You can buy over-the-counter rehydration sachets to dissolve into water. Plain water alone will not restore their balance of electrolytes and too much plain water can further disrupt this balance. You should also avoid giving your child juice or soda as these can worsen their diarrhoea. 

If your child has diarrhoea for a week or more, or they become seriously unwell, see your GP. 

Treating severe diarrhoea

If you have diarrhoea, make sure you stay hydrated. As diarrhoea causes your body to lose water and electrolytes (eg sodium chloride and potassium chloride), it is important to drink rehydration fluids, which are available over the counter as sachets of powdered salts to be dissolved in water.

In general, it is best to let the diarrhoea pass out of your system — especially if it is caused by an infection or toxin — and replace the fluids you have lost rather than taking an antidiarrhoeal medication, which will slow down your digestion. 

However, if you need to travel and, therefore, cannot visit the toilet frequently, you can take an antidiarrhoeal medication in the short term. If you have persistent diarrhoea, it is important to find out the underlying cause before regularly taking an antidiarrhoeal medication.

In severe cases of acute diarrhoea, you may need to have intravenous fluids (ie fluids and salts administered via a small tube (cannula) placed into a vein in your arm) administered in hospital. Vulnerable individuals, such as children and older people, are more likely to need intravenous fluids to treat severe diarrhoea. 

How to prevent diarrhoea

Following good hand hygiene is key to preventing diarrhoea by avoiding infections with viruses or bacteria. You should, therefore, always wash your hands after visiting the toilet and before you eat any food. 

As food poisoning is a common cause of diarrhoea, make sure you properly cook any meat, poultry or seafood and thoroughly wash any raw foods (eg fresh fruits and vegetables). 

You should also avoid contact with anyone who has diarrhoea until their symptoms have resolved.