Common causes of diarrhoea

Diarrhoea is one of those common problems that affects us all from time to time. Yet, sometimes having diarrhoea is a sign of a health problem, or that something in our lifestyle needs to change. Here we explore some of the most common causes of this uncomfortable and inconvenient symptom.

Last updated by Amberley Davis Peer reviewed by Dr Krishna Vakharia

Last updated 8 Jun 2023 Originally published 8 Jun 2023

7 mins read

What is diarrhoea?

Diarrhoea means you have more than three runny poos (stools) in the space of 24 hours. It's usually not serious, but it can be inconvenient, uncomfortable, and unpleasant.

Most people will experience acute diarrhoea at some point. This is where symptoms start up suddenly and typically last for a few days to a couple of weeks at most. Chronic diarrhoea, on the other hand, is when this problem persists and returns in episodes over a long period of time - usually over six weeks.

Symptoms of diarrhoea

Alongside loose or watery stools, there are some other symptoms that often go with diarrhoea. For example, tummy cramps and diarrhoea often go hand in hand. Dehydration can also result from losing lots of fluids through runny stools.

Some common symptoms that occur alongside diarrhoea signal to us that we're unwell. For example:

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Why do I keep getting diarrhoea?

Elouise Rice is The Healthy Gut Dietitian. She explains that there are multiple causes of diarrhoea, and that most are relatively harmless and will clear with time.

"However, some instances of diarrhoea may warrant further testing," says Rice. "If your diarrhoea has lasted longer than seven days, and/or you have blood in your poo, and/or you have unexplained weight loss, you should seek advice from your GP. In general, you should get checked out if you experience any sudden change in your bowel habits - the texture, colour or consistency of your stools - especially if you are over 60."

Diarrhoea for more than three weeks, weight loss, or blood in your poo could indicate more serious problems and you must see a doctor.

Here we explore some of the common causes of acute and chronic diarrhoea.

1. Gut infections

Gut infections are caused by harmful bacteria, viruses, or parasites entering and upsetting your digestive system - also called your gastrointestinal tract. It could be that you've consumed contaminated water or food or that you've come into contact with someone already infected. Diarrhoea is a hallmark symptom of stomach infections, alongside vomiting, tummy pain, dehydration, and fever.

"One of the most common causes of diarrhoea is a stomach infection known as gastroenteritis," says Rice. "This is inflammation of your gut caused by an infection from a bacteria or virus."

If your diarrhoea is linked to gastroenteritis, you may also experience the other possible symptoms of this illness - and they could last anywhere between 1-14 days.

See your doctor if: your symptoms are severe, there's blood in your poo, or you have signs of dehydration that aren't being resolved by drinking lots of fluids.

2. Gut disorders

While gut infections are temporary, gut disorders are long-term gastrointestinal conditions. They need ongoing management to keep the inconvenience and discomfort of diarrhoea and other symptoms to a minimum. Three examples include:

IBS - irritable bowel syndrome

IBS, also called irritable bowel syndrome, is a long-term functional gut disorder that causes episodes of either diarrhoea or constipation as well as bloating and tummy cramps. It's fairly common, affecting one in 10 people of the population worldwide¹.

IBD - inflammatory bowel disease

According to Rice, this long-term condition involving the inflammation of the gut is one of the more serious causes of diarrhoea. Inflammatory bowel disease, or IBD, describes two conditions: Crohn's disease and ulcerative colitis. If you have these conditions, your diarrhoea may contain spots of blood. Other tell-tale signs include unexplained weight loss and tiredness, as well as tummy cramps and bloating.

Diverticulitis

More than three in 10 adults over the age of 50² develop tiny bulges in their colon, known as diverticulosis. These can become swollen and infected - a serious condition known as diverticulitis - which causes diarrhoea and other symptoms such as pain, nausea, and fever.

See your doctor if: you experience repeated episodes of diarrhoea alongside the other symptoms above.

3. Food intolerances

IBS and IBD diarrhoea can be triggered by certain foods, but it's also possible for eating to upset your gut even if you don't have a disorder. Having a food intolerance means that your gut finds it more difficult to digest certain foods. This most often leads to diarrhoea, constipation, wind, bloating, and tummy pain. The most widely experienced food intolerances include:

Lactose intolerance

According to Rice, lactose intolerance is one of the most common diarrhoea-triggering food intolerances. The dietitian explains that people with this condition don't have enough of the enzyme lactase, and this means that they cannot digest lactose - a sugar that's found in milk and dairy products. Most people with lactose intolerance are born with it, but you can develop this condition as a result of chemotherapy or gastroenteritis.

Gluten intolerance

Gluten intolerance is triggered by eating foods that contain gluten, which includes products made with wheat, barley, and rye. The enzyme protease is unable to fully break down gluten and this means that small bits end up in the small intestine. This causes no problems in most people, but in those with gluten intolerance, it results in uncomfortable symptoms.

See your doctor if: you have repeated and frequent episodes of diarrhoea that you believe may be diet-related. Before visiting the GP surgery, it can be helpful to keep a food diary where you track what you eat and when you experience symptoms.

4. Stress and anxiety

"Ever get the runs when you're nervous? This is caused by something called your gut-brain axis³, whereby your brain talks to your gut and causes a stress response - so everything you feel your gut feels too," explains Rice.

If you're visiting the toilet a lot before a job interview or stage performance, stress-induced diarrhoea is perfectly normal and usually short-lived. However, if stress or anxiety is negatively affecting your life and relaxing techniques aren't working, it's important to seek help.

See your doctor if: stress or anxiety is affecting your life, choices, and relationships. They may recommend you for treatments that can help you to cope, like cognitive behavioural therapy (CBT) or medications.

5. Medications

Certain medications can also cause diarrhoea. Antibiotics are a prime example, as these can destroy the beneficial bacteria in your gut, causing an imbalance known as dysbiosis.

Other medications that can sometimes cause diarrhoea include:

Antidepressants.
Proton pump inhibitors - such as omeprazole (Prilosec) and lansoprazole (Prevacid).
Antacids.
Chemotherapy.

Always check the common side effects of any new medication.

See your doctor if: you experience repeated episodes of diarrhoea and have started new medication around the time this started. They may be able to advice alternative medicines.

6. Menstruation

For women who have periods, this is a common time to have acute diarrhoea.

"During menstruation, hormonal changes that cause your uterus to contract can also cause your intestines to do the same thing, resulting in diarrhoea," says Rice.

If this is a nuisance in your life, there are some ways to help prevent menstruation diarrhoea. These include:

Avoiding foods that can make diarrhoea worse - such as spicy foods and caffeine.
Taking birth control pills - although diarrhoea shouldn't be your primary reason for starting this medication.

See your doctor if: the diarrhoea you experience around this time of the month is severe. They can discuss management options and check for other possible health causes.

Common causes of diarrhoea