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What causes diarrhoea


What Causes Diarrhoea & it's Symptoms

Diarrhoea can be unpleasant and inconvenient. Find out what can cause diarrhoea so you can try to prevent it and feel more confident treating it. 

Quick links:


Food and drink

Food intolerances

Food poisoning



Irritable Bowel Syndrome


Stress and anxiety

Diarrhoea is a common problem and one that affects most of us at one time or another. Knowing what can cause diarrhoea makes it easier to treat quickly and could help you avoid getting it from the same source again in the future.

Understanding why and when it’s best to treat diarrhoea can also help you feel confident in yourself. Discover the main causes of diarrhoea.

Diagram explaining diarrhoea causes and how diarrhoea happens

Food and drink

As diarrhoea occurs due to problems with your digestive system and gut – with fluids not being absorbed properly – it’s little surprise that what and how you eat can trigger diarrhoea. Everyone’s body is different, so the food and drink that brings on diarrhoea in someone else may not have the same effect on you.  

However, some foods can be more likely to cause diarrhoea than others. Fatty, greasy and spicy foods can be harder to digest and trigger gut movements. Capsaicin is found in spicy food and can irritate your intestine, speeding up the digestive process and preventing your colon from absorbing enough water.

Drinking alcohol can also cause diarrhoea as it sometimes quickens digestion, preventing water from being absorbed in your colon as normal . If you haven’t eaten, the alcohol can pass through your system even faster. Common eating habits that can also affect your digestive system include:

  • Eating too fast – You’re more likely to overeat and swallow air at the same time, leading to trapped wind. 
  • Eating large, heavy meals – Overeating makes your digestive system work harder.
  • Eating late at night – Your digestive system is at its least efficient at the end of the day.

Some people also experience diarrhoea straight after eating – known as postprandial diarrhoea. You may get an urgent need to use the bathroom and experience bowel pain. If you are concerned about postprandial diarrhoea, speak to your GP as this could be a sign of another condition.

Food intolerances

If you have difficulty digesting specific foods or drinks, you may have an intolerance . Diarrhoea can be a symptom of a number of food intolerances

Common food intolerances that can cause diarrhoea include:

  • Gluten- a protein found in many types of grain, including wheat, rye and barley.
  • Lactose – The body struggles to digest the lactose sugar found in milk and dairy products.

If you think you have a food intolerance or a food allergy, you should visit your GP for advice.

Food poisoning

Food poisoning and diarrhoea generally go hand-in-hand. Diarrhoea is a common symptom of food poisoning, which you can get by ingesting bacteria and viruses from contaminated food or water. These often include:

  • Escherichia coli (E. coli) bacteria
  • Norovirus (See below for more details)

It normally happens if you eat something that wasn’t properly cooked or stored at the right temperature, has been handled by someone with dirty hands or was eaten beyond its ‘use by’ date.

Any kind of food can cause food poisoning, but some of the most common examples include:

  • Raw meat, poultry and fish
  • Fruit and vegetables (unwashed or those washed in contaminated water)
  • Raw eggs and unpasteurised milk

Food poisoning is one potential cause of gastroenteritis and norovirus (see below).

To reduce the risk of catching or spreading food poisoning and diarrhoea, avoid preparing food for others, cook everything thoroughly, wash your hands thoroughly with soap and water, and avoid drinking tap water in locations where it may be contaminated.  

If you have severe diarrhoea, blood in your stools or a high temperature, or if symptoms persist for more than 48 hours consult your doctor and do not use IMODIUM®


A viral or bacterial infection of the gut usually causes gastroenteritis – which is an inflammation of your stomach or bowels. Sometimes known as a stomach bug or traveller’s diarrhoea and commonly linked to food poisoning, its main symptoms include diarrhoea, vomiting and abdominal pains.  

It’s really common and affects around one in five people in the UK every year – so you’re not alone. The main ways you can contract gastroenteritis include:

  • Eating or drinking infected foods containing bacteria, viruses or parasites
  • Directly from another person with gastroenteritis
  • Touching contaminated surfaces

Anyone can be affected by gastroenteritis. Symptoms normally appear up to a day after picking up the infection and, in most cases, last less than a week.

If you experience gastroenteritis and diarrhoea, it’s important that you stay hydrated, have plenty of rest and eat small amounts of plain food if you feel hungry at all, until the symptoms pass. You can also speak to your pharmacist, who may recommend oral rehydration salts to help with dehydration. You can reduce your chance of getting gastroenteritis by practicing good hygiene. This includes washing hands frequently with soap and water, disinfecting surfaces and ensuring food is prepared properly. Flush away any poo or vomit in the toilet and clean the surrounding area. Stay off work for at least 48 hours after the symptoms have passed.

Some vulnerable groups, for example young children, the sick, those with long term medical conditions and the elderly, will need medical advice if they start to experience symptoms of gastroenteritis. You should also seek medical advice if you:

- have fever

- have blood in your stools

- have persistent diarrhoea (If you are considering taking Imodium, seek medical advice first if your diarrhoea has lasted for more than 48 hours).

- are vomiting a lot and can’t keep fluids down

- can't control your bowels

- have signs of dehydration

- have recently travelled abroad

- don’t have someone who can look after you at home and your symptoms are severe

- you are worried about yourself or someone you care for

Imodium over-the-counter medicine is for use in 12 years and over. If you have severe diarrhoea, blood in your stools or a fever, or if your symptoms persist for more than 48 hours, consult your doctor and do not use Imodium®.


Norovirus is estimated to cause around three million cases of gastroenteritis in the UK each year – with the main symptoms being diarrhoea and vomiting.

Also known as the ‘winter vomiting bug’ – as it’s most common from November to early April – the name is deceptive, because you can catch it any time of the year. As it may lead to gastroenteritis, which in itself causes diarrhoea, many of the symptoms are the same and include:

  • Sudden nausea
  • Vomiting
  • Diarrhoea
  • Stomach cramps
  • Headaches
  • Fever
  • Aching arms and legs

Having norovirus is an unpleasant experience, but you should start to feel better in two or three days. There’s currently no specific treatment for norovirus and, as a viral infection, antibiotics will have no effect – although IMODIUM® can help relieve symptoms of diarrhoea.

Norovirus can be spread via contaminated food/surfaces or close contact and is easily contracted by others. For this reason, if you catch norovirus it’s advised you stay off work until at least 48 hours after symptoms have passed to prevent further spread. If you experience norovirus it's important that you stay hydrated. Your pharmacist may recommend rehydration salts if you have signs of dehydration. If you feel like eating, try plain foods such as soup, rice, pasta and bread. Finally, get plenty of rest.  You should also maintain basic hygiene and cleaning to help stop the spread. Wash your hands with soap and water (alcohol hand gels do not kill the virus) and disinfect surfaces that could be contaminated with a bleach based household cleaner. Avoid eating raw unwashed food. Wash any contaminated bedding or clothing separately (at 60oC) and do not share towels or flannels. Flush any poo or vomit in the toilet and clean the surrounding area with a bleached based household cleaner.  Contact your GP or NHS 111 if you're concerned or feel you need advice.

Irritable Bowel Syndrome (IBS)

Irritable bowel syndrome (IBS) affects the digestive system and can cause diarrhoea or constipation and other symptoms that come and go, lasting for varying amounts of time. 

Almost one in five people suffer from IBS in the UK and around one in three IBS sufferers experience diarrhoea. It can cause bowel pain and sensitivity when food passes through the digestive system.

What causes IBS is not yet known. Although it varies from person to person, certain factors such as such as stress, oversensitive nerves in the gut or family history are believed to be linked to the causes of IBS and associated diarrhoea.

If you have IBS, certain factors can trigger symptoms, such as:

  • Eating and drinking specific things
  • Irregular eating habits
  • Stress and anxiety
  • Lack of exercise

Sadly, there is no cure for IBS yet. But changing your eating habits can help you control the symptoms and reduce the chance of you getting diarrhoea. If you think you might have IBS, it is important that you visit your GP, as they can help you manage the condition and rule out other potential causes of your symptoms.


Many women experience gastrointestinal symptoms before, during and after their period, including abdominal pain, gas and diarrhoea.

It’s perfectly normal, as around one third of women go through gastrointestinal symptoms around the time of menstruation. And if you suffer from IBS there’s a higher chance that you may experience diarrhoea around the time of your period.

The exact cause of diarrhoea during periods isn’t known – although many experts believe it’s due to an increased release of prostaglandin hormones before your period starts. These cause contractions so your uterus sheds its lining, but they can also lead to contractions of your intestines, resulting in diarrhoea.

There are no period-specific treatments for diarrhoea, but using IMODIUM® will help reduce your symptoms.

Other steps include:

  • Staying well hydrated to replace lost fluids
  • Eating foods that are high in soluble fibre to help solidify stools
  • Avoiding caffeine, as well as sugary and spicy foods

Stress and anxiety

Your body produces adrenaline and other chemicals when you become stressed or anxious – speeding up your heart rate and blood pressure. Stress may also make your gut muscles work faster, including those in your large intestine.

Faster digestion can mean less fluid is absorbed in your intestines. In some cases, experiencing diarrhoea could even be the first sign of your body telling you that you’re stressed and need to relax.

There can be various causes of stress and anxiety leading to diarrhoea – from being overwhelmed at work to preparing for an important exam or experiencing personal issues. Whatever is causing you to feel stressed, anxious or nervous, cutting your stress levels could reduce your chance of getting diarrhoea.

You can try to reduce your stress levels in a number of ways, including:

  • Staying active
  • Speaking to friends and family
  • Enjoying some ‘me time’
  • Making sure you get enough sleep


IMODIUM® Original

IMODIUM® Original capsules can stop diarrhoea in one dose.


IMODIUM® IBS Relief helps take control of your medically diagnosed IBS diarrhoea.

IMODIUM® Instants

IMODIUM® Instants dissolve instantly on your tongue, so they’re great for when you’re on the go.

IMODIUM® Dual Action

IMODIUM® Dual Action Tablets not only helps stop diarrhoea, but also soothe painful cramps, bloating and wind.

Where to buy IMODIUM®

Where to buy IMODIUM®

It’s easy to find IMODIUM® in supermarkets, chemists and many other shops. You don't need a prescription, so you can buy it over the counter as well as online.