Diarrhoea – Causes, Symptoms and Treatment
Man holding his stomach and standing in front of a toilet  

Diarrhoea is a condition that describes stools that are loose and passed more frequently than what is typical for an individual. Most people will experience diarrhoea at some point in their life, even multiple bouts of diarrhoea - usually due to illness. 

Whilst diarrhoea is normally temporary and can often clear up on its own, the symptoms can be very unpleasant and complications such as dehydration can occur if the diarrhoea is severe. There are ways to manage diarrhoea at home without needing to see a GP, however, if you are experiencing chronic diarrhoea you may need intervention from a doctor to investigate the cause and help you manage the condition long-term. 




Diarrhoea causes stools to be loose and watery, in more severe cases the stools may be liquidised completely. You will also pass stools more frequently and urgently than you usually do. Other symptoms of diarrhoea include:

  • Abdominal pain or cramps
  • Loss of appetite
  • Nausea and vomiting
  • Headache

More severe diarrhoea may be accompanied by a fever, blood in your poo, persistent vomiting, black or dark tarry poo and weight loss. You should see a doctor if any of these symptoms occur, particularly if you have had diarrhoea for more than 7 days, or more than 24 hours in babies. 


Complications - dehydration 


Dehydration can be a side effect of diarrhoea. Your body can lose a lot of water through passing watery stools which can lead to dehydration. You need to replace this lost water by drinking more fluids to avoid becoming severely dehydrated. The very young and the very old are more at risk. 

Look out for the following signs of dehydration and seek medical help if they occur:

  • Feeling tired, lightheaded or dizzy
  • Feeling thirsty
  • Loss of appetite
  • Dry tongue
  • Nausea
  • Sunken eyes
  • Muscle cramps 
  • Rapid heartbeat
  • Peeing less often than normal
  • Dark yellow pee
  • Strong smelling pee

In babies, they may also be irritable or drowsy, have a lack of or no tears when they cry, have infrequent peeing or fewer wet nappies, have cold hands and feet, and pale and mottled skin. 


Causes of diarrhoea


Diarrhoea can be caused by short-term illnesses like food poisoning, but if you have frequent bouts of diarrhoea over a long period of time there may be an underlying chronic condition responsible for this.


Short term illnesses 


Viral, bacterial or parasitic infection


Diarrhoea can be a symptom of viral, bacterial or parasitic infections that affect the gut. This type of infection is called gastroenteritis, or a ‘stomach bug’ as people often call it and it’s the most common cause of acute diarrhoea. Norovirus is the most common viral infection of the gut and is picked up from surfaces and unwashed, raw food. It not only causes watery diarrhoea but it can also cause projectile vomiting which increases the risk of dehydration. This infection lasts two to three days 

Other infections include Escherichia coli (E. coli) (bacterial) and giardiasis (parasitic). Gastroenteritis is often picked up when travelling abroad, particularly in developing countries with poor hygiene. 


Food allergy and intolerance


Certain food intolerances can cause digestive problems including diarrhoea. An intolerance happens because your body is unable to digest a certain type of food or ingredients such as lactose which is commonly found in dairy products, and the side effect of consuming these foods is temporary bowel changes such as diarrhoea, stomach pain, bloating and wind. This is different to a food allergy.

With food allergies, the body’s immune system overreacts and treats the food as a threat. Symptoms of an allergy usually affect the skin, breathing and swallowing but the digestive system can be affected too. 

Keeping a food diary can help you discover what food you are allergic to or intolerant to, and avoiding this will prevent your symptoms. 




Starting a new medication can cause unpleasant side effects for a short while as your body adjusts to it. All medications can potentially cause stomach issues like vomiting and diarrhoea, most notably antibiotics, antacids and some antidepressants. 

Laxatives also make stools looser and watery which is why they are used to treat constipation (dry and hard stools that are difficult to pass). 

Other potential causes of acute diarrhoea include:

  • Stress and anxiety
  • Alcohol
  • Appendicitis 

Long term conditions


Living with a long-term condition such as irritable bowel syndrome (IBS) can mean diarrhoea is a regular occurrence for some people, this is known as chronic diarrhoea.

The following conditions affect the bowel and surrounding areas and can cause persistent diarrhoea.

  • IBS - the gut doesn’t work as it should 
  • Inflammatory bowel disease - an umbrella term to describe conditions that cause the gut to become inflamed such as Crohn’s disease and ulcerative colitis 
  • Coeliac disease - an autoimmune condition that causes the gut to react to gluten adversely
  • Cancer - particularly bowel cancer. Diarrhoea can also occur after some cancer treatments such as radiotherapy and chemotherapy, as well as surgery to remove tumours
  • Chronic pancreatitis - inflammation of the pancreas
  • Diverticular disease - causes bulges on the lining of the intestine
  • Bile acid malabsorption - causes bile to build up in the digestive system

Why do I have diarrhoea after eating?


Diarrhoea can be caused by something you’ve eaten, especially if you have a food intolerance, food allergy, or a bowel condition like IBS, Crohn’s disease, or coeliac disease. In these cases, the best way to treat your diarrhoea will be to manage the condition itself, so make sure to ask your doctor for advice and treatment options. You may also have diarrhoea as a result of food poisoning, which happens if your food isn’t prepared properly or has gone off.


If you don’t have a long-term condition which causes diarrhoea, think about the foods you’ve eaten recently.


Diarrhoea during pregnancy


You can experience diarrhoea during pregnancy, especially during your first trimester when digestive issues are common. All of the changes your body is going through can affect your bowel.


However, you’ll usually find that constipation is much more common during pregnancy than diarrhoea, as all of the excess progesterone in your system slows down your bowel. You should ask your doctor, pharmacist, midwife, or health visitor for advice on how to ease it during your pregnancy.




Acute diarrhoea may be easier to diagnose as it can often come on suddenly after an infection and only lasts a few days. Chronic diarrhoea requires more investigation and can be more difficult to get to the root cause. IBS, for instance, can often be misdiagnosed because the symptoms are so varying and are similar to that of other conditions. 

To diagnose the cause of your diarrhoea your GP will ask questions about any other symptoms that may be present, how long you have had diarrhoea for, what your stools are like, and your lifestyle recently such as if you’ve been experiencing stress, any changes in your diet and whether you have travelled abroad. 

Your GP can perform a number of tests to diagnose or rule out underlying health conditions that may be causing diarrhoea that is lasting more than two weeks. Tests can include stool samples, blood tests, rectal examinations and internal examinations of the bowel if necessary. 

Your pharmacist can help with diagnosing and treating acute diarrhoea.


Seeing a pharmacist


A pharmacist can provide medication to stop diarrhoea for a few hours and also rehydration sachets to prevent dehydration. 


When to call 111/an emergency doctor


Diarrhoea that is severe and persistent and accompanied by the following symptoms should prompt you to call 111:

  • Persistent vomiting
  • Weight loss
  • Blood in your stools
  • Black or dark stools
  • Severe stomach pain
  • Signs of dehydration 
  • A fever

When to go to A&E/call emergency services


The below circumstances mean you need urgent medical attention

  • You may have ingested something poisonous 
  • You are vomiting blood or the blood looks like ground coffee or is green or yellow in colour
  • You have a stiff neck and your eyes are sensitive to bright lights
  • You have a headache or stomach pain that is sudden and severe

Treating diarrhoea 

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You can usually treat mild diarrhoea at home with medication, rest, drinking lots of fluids regularly and eating small, plain meals if you’re able to. 

FyboCalm Diarrhoea Relief capsules are designed to help relieve and prevent recurrent diarrhoea for long-lasting relief. With its prebiotic properties, the formulation helps to stimulate the growth of health promoting bacteria.




Loperamide is the most common and effective anti-diarrhoea medicine available to buy without a prescription from pharmacies and retail stores such as supermarkets. Children under the age of 12 must be prescribed this medicine by a doctor. 

Loperamide works by slowing the speed of food passing through the gut so that water can be drawn from the intestines which make stools more solid. You may only need to take loperamide for a couple of days, any longer than this should be prescribed by your GP. 


Oral rehydration


As your body loses water through diarrhoea you need to keep replacing this loss by drinking lots of water. You can also take rehydration tablets or sachets that you put in water to not only hydrate you but also replace the salts, glucose and essential nutrients that you lose through diarrhoea. 

Many oral rehydration products come in pleasant flavours such as blackcurrant to make it easier to digest. 


Pain relief


Diarrhoea can cause painful cramps and some people experience headaches and fever. Painkillers such as paracetamol and ibuprofen can help ease these symptoms but they won’t treat diarrhoea. 




Antibiotics cannot treat all causes of diarrhoea and they are very rarely used unless the diarrhoea is caused by a specific bacterial infection. 


Foods to eat whilst dealing with diarrhoea


You may not always feel like eating while you have diarrhoea, but if you are able to eat it’s best to stick to a plain diet and avoid spicy foods. A diet known as BRAT is recommended, this consists of bananas, rice, applesauce and toast. 




Preventing diarrhoea can be difficult as it’s often caused by viruses and bacteria that we cannot see, however, practicing good hygiene is the best way to prevent a bout of diarrhoea. 

Here are some tips for preventing diarrhoea: 

  • Wash your hands regularly. Viruses and bacteria can infect the body through hand-to-mouth touching 
  • Take care when preparing food by washing your hands and surfaces, cooking food thoroughly, storing it safely (never storing raw and uncooked food together) and never eating food past its use-by date
  • Disinfect the entire toilet after each use when you have diarrhoea
  • Avoid sharing cutlery and utensils, towels and flannels 
  • Soiled clothing and bedding should be washed separately and at the highest temperature 
  • Do not return to work or school until at least 48 hours after the last episode of diarrhoea 
  • Do not use swimming pools for 2 weeks after the last episode of diarrhoea 
  • If travelling to a developing country where public hygiene is poor do not drink tap water or boil it for at least one minute before drinking. You should also avoid ice cubes, ice cream, raw or uncooked seafood and meat, anything that contains uncooked eggs, unpasteurised dairy products, salads, and fruit and vegetables with damaged skin 
  • Get vaccinated where possible. Children can be vaccinated against rotavirus 
Laura Shillcock - Medical Content Writer
James O'Loan - CEO & Superintendent Pharmacist
James O'Loan , CEO & Superintendent Pharmacist on 21 March 2023
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