This factsheet is about diarrhoea

Most healthy people open their bowels between three times a day and three times a week. Normal stools are usually solid because the small intestine and colon are highly efficient in absorbing nutrients, fluid and salts from the gut contents.

Diarrhoea occurs when these processes are impaired, for example when bacteria or viruses damage the lining of the gut and/or there is excessive secretion of fluid such as water, into the bowel that overwhelms the ability of the gut to reabsorb this fluid and salts. The stools become loose and watery and more frequent bowel movements occur. Diarrhoea is also a symptom of some diseases of the digestive tract. In acute (short lasting) diarrhoea, symptoms come on suddenly but usually clear up within five to 10 days. Chronic (long lasting) diarrhoea continues longer than 4 weeks, and the cause should always be investigated by a GP.


Causes of diarrhoea

There are many reasons why diarrhoea can occur. Common causes include:

  • Intestinal infection (gastroenteritis): this is the most common cause of acute diarrhoea with infants and young children particularly susceptible. Bouts of norovirus diarrhoea often make the news since they can occur in local epidemics.
  • Food poisoning: another common form of acute diarrhoea usually caused by the Salmonella and Campylobacter bacteria. These infections can be passed via contaminated water or food, such as poultry and eggs, or by a carrier (i.e. someone who has the infection but no symptoms).
  • Medications: acute diarrhoea can sometimes occur during or after a course of antibiotics or as a result of other medications which cause the contents of the bowel to move too rapidly through the gut resulting in insufficient time for absorption. It is always worth asking your doctor whether your medications can cause diarrhoea. Laxatives can result in an excessive secretion of fluid into the bowel.
  • Anxiety: as with some medications, anxiety can cause the bowel contents to move too rapidly through the gut.
  • Overactive thyroid: The thyroid gland produces hormones that affect the running of the body, such as regulating heart rate or temperature. If the thyroid produces too many hormones this can cause the body to ‘run’ too quickly, causing diarrhoea, among other symptoms. Overactive thyroid can be diagnosed by a GP using a simple blood test.
  • Irritable bowel syndrome (IBS): bowel frequency is increased in 1 in 3 of those suffering from IBS. IBS is a functional gastrointestinal condition where the large bowel is moving too fast and this doesn’t allow enough time for absorption of fluid and salts, causing diarrhoea. Around 1 in 4 people with IBS-D* may have bile acid diarrhoea.
  • Food intolerance: The main culprit for diarrhoea symptoms due to food intolerance is lactose intolerance, it is caused by reduction in levels of lactase, an enzyme produced in the small bowel that helps digest lactose, the sugar found in milk. It can be as a result of having lower levels of lactose from birth or can occur secondary to other digestive diseases. Fructose intolerance can also occur, although less frequently, resulting in diarrhoea. Please note that blood tests for food intolerances are not used by the NHS because they are ineffective at identifying the cause and can lead to the diet being overly restricted. If you suspect a food intolerance, ask your GP for a referral to a state registered dietitian.
  • Inflammatory bowel disease (IBD): These are a range of autoimmune diseases that result in inflammation of the digestive tract (Crohn’s disease) or only the large bowel in the case of ulcerative colitis.
  • Bowel cancer: diarrhoea is a common symptom, however, a prolonged change in bowel habit lasting more than two or three months should always be investigated. If you have a family history of bowel cancer you should visit your doctor within a few weeks of any changes.
  • Coeliac disease: This is an autoimmune condition where gluten, a protein found in wheat, barley or rye causes damage to the small bowel lining. This results in food not being absorbed into the body and in some cases results in diarrhoea.
  • Microscopic colitis: Microscopic colitis is an inflammatory disease of the bowel which is not visible by looking at the bowel wall with a camera (endoscopy). It is characterised by watery diarrhoea, usually accompanied by urgency and problems with bowel control.
  • Bile acid malabsorption (BAM): this is a disturbance of the cycle of bile acid distribution in the body. Bile acid, produced by the liver, is released into the small bowel to help absorb fats from food. The problem occurs when it does not get reabsorbed at the end of the small bowel. The bile then enters and irritates the tissues of the large bowel generally causing frequent episodes of watery diarrhoea.
  • Pancreatic exocrine insufficiency (PEI): The pancreas has two functions, one of these is to produce digestive enzymes to help digest the food we eat, problems with the pancreas can reduce it’s ability to produce these enzymes. This can result in malabsorption of fats and diarrhoea.
  • Pelvic radiation disease: radiation treatment for cancers of the lower abdomen and pelvis can cause damage to the digestive tract resulting in diarrhoea in some people.
  • Surgery: Any removal of significant parts of the digestive tract can result in diarrhoea, sometimes this can also cause dumping syndrome. Ask your surgeon for further advice.
  • Dumping syndrome: this usually happens after surgery to the digestive tract and is where food is released too quickly from the stomach causing excess fluid in the small intestine and altering hormone levels, resulting in diarrhoea.

There are other causes for diarrhoea to occur, but these are generally much rarer.


What are the usual symptoms of diarrhoea?

Diarrhoea is commonly associated with cramping pain in the central or lower abdomen. If this is caused by infections or inflammatory bowel disease it may cause fever. Infections due to Shigella and Campylobacter that get into the lining of the bowel and cause acute inflammation and fever. When there is direct damage to the bowel, blood may be associated with the diarrhoea, which is known as dysentery when it has an infective cause, plus blood in stools is common symptom with ulcerative colitis, a type of IBD.

How is diarrhoea diagnosed?

Most episodes of acute diarrhoea get better without the need for specific medical advice. However, if you are a food handler then you should always consult your doctor and inform your employer. Otherwise you should seek medical advice if any of the following apply:

  • If diarrhoea persists for more than 14 days
  • If you notice blood in the diarrhoea
  • If you develop a high fever
  • If your cramping and abdominal pains become severe and constant

The doctor will want to talk to you about your symptoms to try to identify a cause. The doctor will also want to physically examine your abdomen and possibly your back passage. The priority at this stage is to ensure that your stool is checked to determine whether there are any infective agents present that might be the cause of the diarrhoea and your other symptoms. Another test, available to some GPs, is called a faecal calprotectin test, a stool test that identifies inflammation in the digestive tract normally due to IBD, IBD can also be checked for using simple blood tests, if the calprotectin test is not available. The doctor may also do some other blood tests to rule out other causes, such as coeliac disease. It is very important that you do not stop eating sources of gluten, wheat, barley and rye (bread pasta and wheat containing breakfast cereals) before you see your GP, as you need to have gluten antibodies in your system, to correctly identify coeliac disease.


How is acute diarrhoea treated?  

Most episodes of acute diarrhoea will settle within a few days without any intervention. However, if the episode is severe there are several treatments that can help.

Rehydration: ensure that enough additional fluids and salts are taken to replace those lost in the diarrhoea. For infants, young children and the elderly, who are more sensitive to fluid losses, it is wise to use a pre-prepared oral rehydration solution, which can be purchased over the counter in most pharmacies. For most adults, oral rehydration can usually be achieved simply by increasing fluid intake in the form of mineral water, fruit juices (which also contain potassium) and salty soups (sodium), together with some form of carbohydrate (rice, pasta, salty crackers), which is important for promoting fluid and salt absorption.

Food intake: there is no need to stop eating although sufferers often prefer a lighter diet in the early phase of the illness. There is no need to interrupt breast-feeding for breast-fed infants. Bottle-fed infants should still receive full-strength formula milk. In general, for adults, avoidance of dairy products and spicy foods short term during the initial phase of illness until foods are well tolerated again. Any problems in tolerating dairy products long term needs to be reported to your doctor.

Medication: an anti-diarrhoea drug such as loperamide is available from pharmacies without prescription. This is often helpful early in the illness to reduce bowel frequency. However, it should not be used in infants and very young children because of concerns that is may depress respiration.

Antibiotics: for travellers with severe diarrhoea for whom the loss of one or two days would seriously affect their activities, the severity and duration of the illness can be dramatically reduced by taking a short course, or even a single dose of broad-spectrum antibiotic.


One of the most important and basic ways to avoid it is by careful handwashing after using the bathroom and before consuming food. Because most acute diarrhoea is related to intestinal infection that is usually transmitted by contaminated food or water, then it is possible to avoid an illness by being scrupulously careful about food and fluid intake. Only drink bottled or boiled water and avoid ice cubes when the origin of the water is uncertain. Avoid raw, unpeeled fruits and salads, shellfish and all foods that might contain raw egg. The safest food is that which is hot and well cooked. Bouts of diarrhoea due to norovirus occur in local epidemics, and it is important not to spread infection, so avoid visiting hospitals and unwell relatives at such times.


Hygiene measures as outlined above should always be the first line protection against acute diarrhoea. However, there are some other measures that may help to reduce the chances of being affected.

Antibiotics: for those travelling to high-risk areas (such as Indian sub-continent, South East Asia, Africa and Latin America) the chance of experiencing an attack of acute diarrhoea can be reduced by taking a broad-spectrum antibiotic. However, this is not generally advised because antibiotics do have adverse effects and widespread use in this way can lead to the emergence of antibiotic resistance. There is a danger, therefore, that the treatment might be worse than the disease.

Vaccines:  vaccines for traveller’s diarrhoea are under development and one moderately effective vaccine is now available in the United Kingdom (Dukoral). It is aimed at a type of bacteria known as enterotoxigenic Escherichia coli (E.coli), which is the most common cause of traveller’s diarrhoea.

Probiotics: there is some evidence that probiotics (such as lactobacilli and bifidobacteria) found in ‘live yoghurts’ and other preparations may also reduce the chances of experiencing an episode of infective diarrhoea. In addition, over the counter medications may also be useful and your pharmacist can advise you.


Treatment of chronic diarrhoea will vary and will depend on the cause of the diarrhoea.


Does diarrhoea need to be monitored and if so, how?

Most episodes of acute diarrhoea will settle spontaneously without the need for any medical treatment. However, if it persists, you may also be referred for an endoscopy, where a flexible tube with a camera is passed into the bowel via the anus, to determine whether there is any inflammation in the rectum or colon (colitis). In addition, if your stool tests show any sign of infection this may be treated with antibiotics or further investigations. For episodes of chronic diarrhoea, the cause will be identified, and monitoring will vary depending on the cause of the diarrhoea.

What to ask your doctor?

  • Could my diarrhoea be caused by any medications I am currently taking and, if so, is there an alternative?
  • Are there any over the counter treatments I can take?
  • Do I need my stools checked?
  • Do I need to have any other tests to identify the cause of diarrhoea that lasts longer than 10 days?


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