This factsheet is about diarrhoea

This factsheet explains what diarrhoea disorders are. When it is a problem needing you to tell your doctor about it and what treatment is available.

Many healthy people open their bowels between three times a day and three times a week. Normal poo is usually solid. This is because the small and large bowel are good at taking in nutrients and fluids.

Diarrhoea can occur when one or more of these processes become faulty. Examples include:

  • When bugs like bacteria or viruses damage the lining of the gut.
  • When there is excessive fluid secretion into the bowel.

Sometimes both examples occur. More liquid overwhelms the gut’s ability to reabsorb the fluid and salts. The poo becomes loose and watery. Bowel movements happen more often. Diarrhoea is also a symptom of some diseases of the digestive tract. In acute diarrhoea, symptoms come on quickly and last a short time. Acute diarrhoea symptoms usually clear up within 5 to 7 days.

Diarrhoea that is chronic lasts a longer time. It generally lasts 4 weeks or more. You should always see your GP if the diarrhoea lasts a long time. They will investigate the cause.


Causes of diarrhoea

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

  • Bowel infection (gastroenteritis). This is the most common cause of acute diarrhoea. Infants and young children are particularly susceptible. Norovirus diarrhoea often makes the news. It can occur in local epidemics. Diarrhoea caused by a virus can last anywhere from 2 to 3 days.
  • Food poisoning. This is another type of bowel infection. Contaminated food or water causes food poisoning. The contamination is by bacteria. Common types are Salmonella or Campylobacter. Some foods that might include the bacteria are poultry and eggs. A carrier is someone who has the infection but no symptoms. They can also spread the infection. Food poisoning can last about 3 to 7 days without treatment.
  • Medicines. Diarrhoea can occur during or after a course of antibiotics. Other medicines may also cause diarrhoea. Medicines can cause the bowels to move too fast. This results in too little time for absorption. Some laxatives can cause too much fluid in the bowel. Ask your doctor if your medicine can cause diarrhoea. Do not stop taking any medicine your doctor has recommended. Talk to your doctor first.
  • Anxiety. Anxiety and stress can speed up bowel movements. This can cause diarrhoea.
  • Overactive thyroid. The thyroid gland produces chemicals (hormones). These help control the running of the body. Examples are regulating heart rate or temperature. If the thyroid produces too many hormones this can cause the body to ‘run’ too fast. This is a less frequent cause of diarrhoea than the other causes listed. Overactive thyroid happens more in women. It happens less in men. Overactive thyroid also affects those who have undergone gender reassignment but there is no UK data for how many are affected. Your GP can diagnose Overactive thyroid using a simple blood test.
  • Irritable bowel syndrome (IBS). Approximately 1 in 3 people with IBS have diarrhoea. IBS is a disorder of gut-brain interaction (DGBI). In people with IBS and diarrhoea (IBS-D) the bowel contents pull fluid from the body as they pass through. This means there is too much fluid in the poo to be absorbed. About 1 in 5 people with IBS-D symptoms may have bile acid diarrhoea. About 1 in 10 people with IBS-D symptoms may have microscopic colitis. In most cases, a gastroenterologist can tell IBS from bile-acid malabsorption and microscopic colitis. They do this by taking a thorough clinical history. Tests also diagnose bile acid diarrhoea and microscopic colitis.
  • Food intolerance. The most common food intolerance is lactose. 8 in 100 people might have lactose intolerance in the UK. This is the same as 8 people being diagnosed in small village. It is caused by a reduction in levels of an enzyme called lactase. The small bowel produces it. Lactase helps digest lactose, the sugar found in milk. Lactose intolerance sometimes happens because of lower levels from birth. It can also occur due to other digestive diseases. There are other intolerances. They include fructose intolerance.
  • Many companies sell intolerance tests. They claim to help people find food intolerances. Some examples of these tests include the IgG blood test. Also, kinesiology, hair analysis, or the pulse test also claim to test food intolerances. You should avoid these tests as they have no solid scientific basis. They are not recommended to diagnose food intolerance by the NHS. The best way to diagnose a food intolerance is by monitoring symptoms. You do this when you eat certain foods. A dietitian should oversee this approach. This is so that the process avoids a very restricted diet.
  • Pancreatic exocrine insufficiency (PEI). The pancreas has 2 functions. One of these is to produce digestive enzymes to help digest the food we eat. Pancreas problems can reduce its ability to make them. This can result in malabsorption of fats and diarrhoea. The poo might be greasy and difficult to flush.
  • Inflammatory bowel disease (IBD). These are a range of autoimmune diseases. In them, the body attacks its own tissues. In people with Crohn’s disease, inflammation can affect all the digestive tract. The digestive system goes from the mouth to the anus. People with ulcerative colitis have inflammation. But it only affects the large bowel.
  • Bowel cancer. Diarrhoea can be a symptom of bowel cancer in some people. Particularly those people who have risk factors. Bowel cancer is more common in the following people:
    • Those above the age of 50.
    • Cigarette smokers.
    • People who have a higher than healthy body weight.
    • People with a have a family history of bowel cancer.
  • The health service has a program to screen for bowel cancer. To be eligible to receive the test there are certain standards to meet. They are different across the four countries of the UK. People who are eligible will get a bowel cancer testing kit in the post every 2 years. They must be registered with a GP to receive one.
  • Coeliac disease. This is an autoimmune condition. When gluten is eaten, it causes symptoms. Gluten is a protein that is found in wheat, barley and rye. Gluten harms the lining of the small bowel. This results in food passing through the body and not being used.  In some people, coeliac disease can result in diarrhoea.
  • Microscopic colitis. This is an inflammatory disease of the bowel, which is not visible by looking at the bowel wall with a camera (colonoscopy). 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, made in the liver, is released into the small bowel to help break down fats in food. The problem occurs when it does not get taken back into the body at the end of the small bowel. The bile then causes watery diarrhoea when it reaches the large bowel.
  • Pelvic radiation disease. Radiation treatment can harm the digestive tract. This happens during cancer treatment. The cancers where this happens are of the lower belly and pelvis. This is a cause of diarrhoea in some people.
  • Surgery. Removal of large parts of the digestive tract can result in diarrhoea. Ask your surgeon for further advice.
  • Dumping syndrome. This is a disorder of gut-brain interaction. It is like IBS. But the diarrhoea occurs without major belly pain.
  • Functional Diarrhoea. This is a disorder of gut-brain interaction. It is like IBS. But the diarrhoea occurs without major belly pain.

Other medical conditions can cause diarrhoea, but they are much rarer. Rare means between 1 in 10,000 and 1 in 1000 people. This is equivalent to 1 person in a small town being diagnosed with a condition.


What are the usual symptoms of diarrhoea?

Diarrhoea may cause cramping pain. The pain is in the centre or lower belly. People can get bowel infections. They can have inflammatory bowel disease. Both conditions can cause diarrhoea and fever.

Infections due to Shigella and Campylobacter bacteria can harm the bowel lining. This can cause acute inflammation and fever. Symptoms could also include diarrhoea and blood in poo. Doctors call these symptoms dysentery. They only do so if an infection caused them.

Blood in poo can be a symptom of ulcerative colitis, a type of IBD. You might also want to check Guts UK tool PooTorial.

How is diarrhoea diagnosed?

Most acute diarrhoea symptoms get better. They don’t need specific medical advice. But, if your job is handling food, you should contact your doctor. You should also tell your employer. But, if the episode is severe there are several treatments that can help. Otherwise, seek medical advice from NHS 111 if any of these apply:

  • If diarrhoea lasts for more than 7 days.
  • If you notice blood in the diarrhoea.
  • If you develop a high fever.
  • If your cramping and belly pains become very bad and constant.
  • If you or a child is still dehydrated after using rehydration sachets.

Some more vulnerable groups may need to seek advice sooner. Babies are vulnerable. So are young children and older people. Dehydration can cause dark coloured urine to occur. A dehydrated baby might have fewer wet nappies.

The doctor will want to talk to you about your symptoms to try to identify a cause. The doctor will also want to examine your belly. They might also check your back passage. The priority is at this stage is to ensure that your poo is tested. This is to see if there are any bugs in it that could cause infection and diarrhoea.

It might be challenging to collect a sample if your diarrhoea is severe. See the NHS website for advice. Or contact Guts UK or call 0207 4860341 if you would like a copy.

Faecal calprotectin test. Another test is available to some GPs. It is called a faecal calprotectin test. This is a poo test that shows inflammation in the digestive tract, due to IBD. Simple blood tests can also check for IBD. This is used if the calprotectin test is not available.

Faecal elastase test. This test can diagnose pancreatic exocrine insufficiency.

Blood test. The doctor may also do other blood tests. They are to rule out other causes, like coeliac disease. It is very important that you do not stop eating sources of gluten before you see your GP. Gluten comes from wheat, barley, and rye. It’s in bread, pasta, and wheat-based cereals. This is because the blood needs gluten antibodies for a diagnosis. Some people with bowel cancer may have low blood iron levels. This is called anaemia. Your GP can test your blood for anaemia.


How is acute diarrhoea treated?  

Most cases of acute diarrhoea will clear up in a few days. They will do so without medical treatment. But, if the episode is severe there are several treatments that can help.

Rehydration. Ensure you have extra fluids and salts. You need them to replace those lost in the diarrhoea. Some groups are more sensitive to fluid loss. Examples include:

  • Babies.
  • Young children.
  • Older people.

For these groups it is a good idea to use a pre-prepared oral rehydration solution. You can buy it over the counter in most pharmacies. For many adults, you can treat dehydration by drinking more fluid. Suitable choices include:

  • Mineral water.
  • Salty soups (which also contain sodium another type of salt).

Have the fluids with starchy carbs like rice, pasta, or crackers. This can help the fluid and salt absorb into the body.

Food intake. There is no need to stop eating. Although people often prefer a lighter diet in the early stage of the illness. Breast-fed infants don’t need to stop breast-feeding. Give bottle fed infants full strength formula.  It might help some adults to avoid dairy, alcohol, and spicy foods. They should do this during the early stages of diarrhoea. Adults should begin eating their usual diet once it is tolerated. Report any long term problems with dairy products to your doctor.

Medicine. Anti-diarrhoea medicine is available from pharmacies. An example is loperamide. You do not need a prescription to buy it. This is often helpful early in the stage of the diarrhoea. It helps to reduce the frequency of bowel opening. Do not give loperamide to children under 12 children. This is because of concerns that it may slow down breathing.

Antibiotics. Travellers with bad diarrhoea can find their holiday spoiled. But usually, symptoms last only 1 or 2 days. Travellers who are unwell should seek the help of a medical doctor. The doctor may give you antibiotics. This depends on your health and circumstances. Note that diarrhoea can be an antibiotic side effect. This should usually get better once the course ends. Discuss this with a doctor or your GP if you are concerned.


One of the most important ways to avoid acute diarrhoea is by handwashing. This is especially true after using the toilet and before eating.

Many cases of acute diarrhoea are related to a bowel infection. This is usually caused by contaminated food or water. It is possible to avoid an illness by being very careful about food and fluid intake. This might be advice to follow when traveling. When water is impure, it may be safer to drink bottled or boiled water. People should also avoid ice cubes when the cleanliness of water is not clear. Also avoid the following:

  • Raw, unpeeled fruits and salads.
  • Shellfish.
  • Foods that might contain raw egg.

The safest foods are those which are piping hot and well-cooked.

Norovirus causes diarrhoea. It occurs in sudden local outbreaks. It is important not to spread the infection. So, during that time avoid visiting:

  • Hospitals.
  • Older people’s homes.
  • Schools.
  • Unwell relatives.

The earlier tips on hygiene should come first. They can protect against acute diarrhoea. But other treatments may help. They can cut the chances of getting acute diarrhoea.

Antibiotics. A doctor may prescribe antibiotics. This happens when the acute diarrhoea is caused by bacteria. Antibiotic overuse leads to resistance. So, take them only with medical advice. Antibiotics may also cause diarrhoea. It is a side-effect. This should usually get better once the course ends. Discuss this with a doctor or your GP if you are concerned.

Vaccines. There are new vaccines for traveller’s diarrhoea. The United Kingdom now has one effective vaccine. It’s called Dukoral. It’s use prevents one type of bacteria that causes the illness cholera. It helps approximately 8 people in 10. If you are travelling to risky areas, your doctor can offer it to adults and children over 2.


Treatment of chronic diarrhoea varies. It will depend on the cause of the diarrhoea.


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

Many cases of acute diarrhoea will settle on their own. People who have chronic diarrhoea should seek help from their GP. Doctors should base the number and type of tests on a person’s history and exam. Some people may need a blood test. It checks for anaemia or rules out coeliac disease. They may also need a poo sample test. It tests for infection. Others may need an endoscopy, a camera test. An endoscope allows a doctor to see if there are any problems with the large bowel. These problems could be due to inflammation or cancer.

What to ask your doctor?

  • Could my diarrhoea be caused by any medicines I am currently taking.  If so, is there an alternative?
  • Are there any over the counter treatments I can take?
  • Do I need my poo checked?
  • Do I need any more tests? They could find the cause of diarrhoea that lasts over 7 days.

The What’s Up With My Gut website makes the process of diagnosis easier to understand and less overwhelming, with step-by-step guides to support you to understand the actions your GP might take. This can help you to get the best out of your GP appointments and understand which conditions your GP might look into and what tests or investigations they might consider.


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Copyright © 2024 Guts UK.

This leaflet was published by Guts UK charity in 2024 and will be reviewed in 2026. The leaflet was written by Guts UK and reviewed by experts in diarrhoea and has been subject to both lay and professional review. All content in this leaflet is for information only. The information in this leaflet is not a substitute for professional medical care by a qualified doctor or other healthcare professional. We currently use AI translation tools on our website, which may not always provide perfect translations. Please check for further explanation with your doctor if the information is unclear. ALWAYS check with your doctor if you have any concerns about your health, medical condition or treatment. The publishers are not responsible or liable, directly or indirectly, for any form of damages whatsoever resulting from the use (or misuse) of information contained or implied in this leaflet. Please contact Guts UK if you believe any information in this leaflet is in error.