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Diarrhoea, from a 24-hour bug to something the specialist should see.

Most diarrhoea is short-lived and gets better with fluids and time. The job of this guide is to help you spot the times it isn’t - and to know exactly what to do next.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, BSG and UKHSA sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on acute gastroenteritis, C. difficile, IBS, IBD, coeliac disease and bile acid diarrhoea.

Key facts

Diarrhoea at a glance.

The essentials, in plain English - the definition, the three duration bands and how UK teams work through the differential.

  • What it is

    Passage of loose or watery stools three or more times a day, or a change that is abnormal for you.

  • Acute

    Under 14 days, usually infectious - viral, bacterial or parasitic. Most settle with fluids and time.

  • Persistent

    14 to 30 days - often post-infectious, parasitic (Giardia), or the first sign of a chronic condition.

  • Chronic

    Over 30 days - needs specialist assessment for IBS, IBD, coeliac disease, bile acid diarrhoea and other causes.

  • Red flags

    Blood, mucus, dehydration, fever, weight loss, nocturnal stools and immunocompromise all raise the stakes.

  • First-line care

    Oral rehydration, careful hand hygiene and honest safety-netting - not routine antibiotics.

Why this guide matters

A common symptom with a wide differential.

From viral gastroenteritis to coeliac disease, IBD, bile acid diarrhoea and colorectal cancer - the same symptom can hide very different diagnoses.

  • Most acute cases are self-limiting

    Viral gastroenteritis and food-borne toxins settle in a few days with fluids, rest and good hand hygiene.

  • Duration reshapes the workup

    Once symptoms cross two weeks, the differential shifts toward parasites, IBS, IBD, coeliac disease and bile acid diarrhoea.

  • Red flags change the plan

    Blood, weight loss, nocturnal stools, immunocompromise or a positive FIT test move things onto a specialist pathway.

How the diagnosis is made

From first symptoms to a clear plan.

The steps a UK GP or gastroenterologist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and duration

    Onset, frequency, character, travel, food, antibiotics, immunocompromise and any family history of coeliac disease or IBD.

  2. 02

    Assessing

    Examination and hydration

    Vitals, capillary refill, mucous membranes, abdominal exam, weight and PR when clinically indicated.

  3. 03

    Assessing

    Safety-netting for red flags

    Blood, mucus, fever, nocturnal stools, weight loss, tenesmus, dehydration or immunocompromise trigger urgent workup.

  4. 04

    Confirming

    Stool tests

    Culture, microscopy for ova and parasites, C. difficile toxin and faecal calprotectin where inflammation is suspected.

  5. 05

    Confirming

    Bloods and coeliac serology

    FBC, U and Es, LFTs, CRP, TFTs, ferritin, tissue transglutaminase, faecal elastase and a FIT test where appropriate.

  6. 06

    Specialist

    Specialist gastroenterology

    Persistent or chronic diarrhoea, positive calprotectin, weight loss or red flags warrant referral for colonoscopy and biopsies.

  7. 07

    Specialist

    Targeted investigations

    SeHCAT for bile acid diarrhoea, hydrogen breath tests for lactose, fructose or SIBO, and CT or MRI where imaging is needed.

Typical timeline: acute cases settle in days; chronic workup takes weeks, not months.

Symptoms

What diarrhoea actually looks like.

The pattern beyond the loose stool - urgency, cramp, blood, fever, weight loss and the features that tip the diagnosis one way or another.

  • Loose or watery stools

    Three or more a day, or a persistent change from your normal pattern - the defining feature of diarrhoea.

  • Urgency and frequency

    A sudden, hard-to-defer need to open the bowels - a hallmark of both infective and inflammatory causes.

  • Cramping and bloating

    Colicky lower abdominal pain, often eased by opening the bowels - common in IBS, gastroenteritis and IBD.

  • Blood or mucus

    Visible blood or mucus is never normal - think dysenteric infection, IBD, ischaemia or colorectal cancer.

  • Fever and systemic upset

    Fever, rigors or feeling systemically unwell point to invasive infection or an acute inflammatory flare.

  • Nocturnal diarrhoea

    Waking at night to open the bowels is a red flag - organic disease is far more likely than functional.

  • Weight loss and steatorrhoea

    Unintended weight loss or pale, greasy, hard-to-flush stools suggest malabsorption, coeliac disease or pancreatic insufficiency.

  • Red flag - dehydration

    Dry mucous membranes, reduced urine output, dizziness or confusion need urgent rehydration - hospital care if severe.

Treatment

How diarrhoea is treated in the UK.

Rehydration first, targeted antimicrobials only when they help, and specialist-led therapy for chronic causes like IBD, coeliac disease and bile acid diarrhoea.

  • Oral rehydration solution

    Dioralyte or WHO ORS replaces water, salts and glucose - the foundation of care for almost every acute case.

  • IV fluids for severe dehydration

    When oral intake is not possible or dehydration is severe - hospital-based rehydration and electrolyte correction.

  • Loperamide

    Short-term relief for non-bloody, non-febrile acute diarrhoea in adults - avoid in dysentery, C. difficile and children under six.

  • Targeted antibiotics

    Azithromycin for severe Campylobacter or traveller's diarrhoea; metronidazole or tinidazole for Giardia; vancomycin or fidaxomicin for C. difficile.

  • Probiotics

    Saccharomyces boulardii can shorten antibiotic-associated and C. difficile diarrhoea - a useful adjunct, not a cure.

  • Faecal microbiota transplant

    The best-evidenced option for recurrent C. difficile - specialist-led, effective and increasingly available in the UK.

  • Bile acid sequestrants

    Colestyramine or colesevelam for confirmed bile acid diarrhoea - often transformative once the diagnosis is made.

  • Treat the underlying condition

    Gluten-free diet for coeliac disease, IBD-directed therapy, IBS management or endocrine treatment for hyperthyroidism.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or gastroenterologist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE CKS. Diarrhoea - adult's assessment.

  • NICE NG12. Suspected cancer: recognition and referral.

  • British Society of Gastroenterology. Guidelines on the investigation of chronic diarrhoea.

  • UK Health Security Agency. Management of gastrointestinal infections.

Red flags

When diarrhoea needs urgent attention.

Most diarrhoea is manageable at home or in primary care. These are the situations that aren’t - and where escalation matters.

  • Severe dehydration

    Reduced urine output, dizziness, confusion or shock need urgent IV rehydration - call 111 or attend A and E.

  • Bloody diarrhoea

    Visible blood, especially with fever or systemic upset, needs same-day assessment - think dysentery, IBD or ischaemia.

  • Suspected C. difficile

    Recent antibiotics with new diarrhoea - test for C. difficile toxin, avoid loperamide and follow UK infection-control guidance.

  • Weight loss or nocturnal stools

    Neither is functional - both push chronic diarrhoea toward IBD, coeliac disease, malabsorption or malignancy.

  • Immunocompromise

    Chemotherapy, biologics, transplant or HIV - lower the threshold for investigation, imaging and specialist input.

  • Recent travel

    Tropical or resource-limited travel widens the differential to parasites, cholera, typhoid and hepatitis A - test and treat accordingly.

  • STEC O157 and HUS

    Bloody diarrhoea with acute kidney injury - do not give antibiotics or loperamide, escalate to specialist paediatric or renal care.

  • Two-week wait for cancer

    Persistent change in bowel habit with weight loss, iron-deficiency anaemia or a positive FIT test triggers NICE NG12 referral.

  • Post-Campylobacter complications

    Guillain-Barré syndrome and reactive arthritis can follow - new weakness, numbness or joint pain needs urgent review.

Living with it

A common symptom, with a sensible plan.

Four things that make the biggest difference day to day - rehydrate first, eat when you can, protect the people around you and know when to escalate.

A quiet reminder

Time is a treatment - but not for everything.

Most acute diarrhoea settles inside a week. Anything that persists, bleeds, wakes you up or drops your weight deserves a doctor, not another packet from the chemist.

  1. 01 Fluids

    Rehydrate first, always

    Small, frequent sips of oral rehydration solution beat any single intervention - keep going until urine is pale.

  2. 02 Food

    Eat when you can

    Return to a bland, balanced diet as soon as appetite allows - the old BRAT diet is a starting point, not a rule.

  3. 03 Hygiene

    Hand hygiene stops spread

    Soap and water beat alcohol gel for norovirus and C. difficile - and stay off work or school for 48 hours after symptoms settle.

  4. 04 Escalate

    Don't sit on chronic symptoms

    Diarrhoea lasting more than a fortnight, or any red flag, deserves a proper workup - not another packet of Imodium.

Frequently asked

Everything we get asked about diarrhoea.

Quick answers on loperamide, C. difficile, traveller’s diarrhoea and when to worry.

  • What counts as diarrhoea?

    Passage of loose or watery stools three or more times in a day, or a persistent change that is abnormal for you. Acute diarrhoea lasts under 14 days, persistent 14 to 30 days and chronic more than 30 days - each has a different differential and workup.

  • When should I see a doctor?

    Same-day assessment for blood in the stool, severe dehydration, high fever, severe abdominal pain, or diarrhoea in someone who is immunocompromised, pregnant or elderly. GP review for symptoms lasting more than a week, unintended weight loss, nocturnal stools or recent antibiotic use.

  • Should I take Imodium (loperamide)?

    Loperamide can help short-term, non-bloody, non-febrile acute diarrhoea in adults - useful for travel or work commitments. Avoid it in bloody diarrhoea, suspected C. difficile or dysentery, and never give it to children under six. It treats symptoms, not the cause.

  • What is C. difficile diarrhoea?

    A toxin-producing bacterial infection that typically follows antibiotic use, especially in older or hospitalised patients. Treatment is with oral vancomycin or fidaxomicin, and recurrent cases often respond to faecal microbiota transplant. Loperamide should be avoided.

  • Do I need antibiotics for traveller's diarrhoea?

    Most cases are self-limiting and settle with oral rehydration. Severe, febrile or dysenteric illness may warrant a short course of azithromycin or rifaximin - a topic worth discussing with a travel clinic before you leave.

  • When is diarrhoea a sign of something serious?

    Chronic diarrhoea, blood, mucus, weight loss, nocturnal symptoms, iron-deficiency anaemia or a positive FIT test can point to IBD, coeliac disease, bile acid diarrhoea or - rarely - colorectal cancer. NICE NG12 sets out the two-week wait pathway.

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