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Why Does My Dog Have Diarrhoea?
What's causing it, what to watch for, and when to call your vet.
Quick Answer
- Diarrhoea in dogs is common and often mild, but it can also be a sign of something serious.
- Common causes include dietary changes, eating something unsuitable, stress, infections, and parasites.
- Blood in the stool, a puppy with diarrhoea, or any sign of serious illness always needs prompt veterinary attention.
- Diarrhoea alongside vomiting can cause dehydration quickly — don't wait if your dog is also unwell.
- If symptoms haven't improved within 24 to 48 hours in an otherwise well adult dog, contact your vet.
Most dogs have diarrhoea at some point. A single episode in an otherwise alert, active adult dog isn't always cause for alarm, though it does need monitoring. The difficulty is that diarrhoea has a long list of possible causes — some minor, some serious — and a few need prompt attention rather than a wait-and-see approach.
Acute vs Chronic Diarrhoea
Acute diarrhoea comes on suddenly and usually lasts a short time — hours to a couple of days. Chronic diarrhoea persists for weeks or keeps coming back. Both need veterinary attention if they're severe or don't resolve; chronic diarrhoea always warrants a full examination to identify the underlying cause.
Common Causes of Diarrhoea in Dogs
01 Dietary Indiscretion
Dogs eat things they shouldn't. Rubbish, scraps, spoiled food, dead animals on walks, garden compost — any of these can irritate the gut and cause diarrhoea. A single episode in an otherwise well dog often clears up on its own, but repeated or severe symptoms need veterinary attention.
02 Sudden Diet Change
Switching food too quickly is a very common trigger. A dog's digestive system needs time to adjust to a new diet. Gradual transitions over seven to ten days — mixing the old food with increasing amounts of the new — help prevent digestive upset. Many pet food manufacturers include a recommended changeover guide on their packaging.
03 Food Sensitivity or Intolerance
Some dogs have sensitivities to specific ingredients. Common culprits include beef, chicken, dairy, wheat, and artificial additives, though any food component could in theory be involved. Food-related diarrhoea tends to be recurring rather than a one-off and often improves with a supervised elimination diet guided by your vet.
04 Stress or Anxiety
Stress-related diarrhoea is recognised in dogs. It can be triggered by a change in routine, travel, kennelling, loud events such as fireworks, or the arrival of a new pet or person in the household. This type of diarrhoea often resolves once the stressor passes, but recurring stress-linked gut problems are worth discussing with your vet.
05 Bacterial or Viral Infection
Bacterial infections (such as Campylobacter or Salmonella) and viral infections can all cause diarrhoea. These are often accompanied by lethargy, loss of appetite, and sometimes vomiting. The severity varies considerably. If your dog is clearly unwell or symptoms aren't improving, see your vet rather than waiting.
06 Intestinal Parasites
Worms — including roundworm, hookworm, and whipworm — can all cause diarrhoea, as can protozoan parasites such as Giardia and Coccidia. Giardia in particular is relatively common in UK dogs and is picked up from contaminated water or soil. Regular worming addresses common worms, but Giardia and Coccidia need specific diagnosis and treatment from your vet.
07 Pancreatitis
Inflammation of the pancreas can cause diarrhoea alongside vomiting, abdominal pain, and lethargy. Fatty food is a known trigger — rich table scraps and fatty offcuts of meat are best avoided. Pancreatitis ranges from mild to severe and always needs veterinary assessment.
08 Medications
Diarrhoea is a recognised side effect of some medications, including antibiotics. If your dog develops diarrhoea shortly after starting a new medicine, contact your vet. Don't stop prescribed medication without speaking to them first — they may be able to adjust the dose or suggest a way to manage the side effect.
09 Inflammatory Bowel Disease (IBD)
IBD is a chronic condition involving ongoing inflammation of the digestive tract. It tends to cause recurring diarrhoea, sometimes with weight loss, vomiting, and a generally poor coat or condition. IBD requires veterinary diagnosis — often including biopsy — and ongoing management. It can't be resolved at home.
10 Acute Haemorrhagic Diarrhoea Syndrome (AHDS)
Previously called haemorrhagic gastroenteritis (HGE), AHDS causes sudden, severe, bloody diarrhoea — sometimes described as raspberry-jam-like in appearance. It can lead to rapid dehydration and deterioration. The cause isn't always identified, and it can affect any dog, though small breeds appear to be at higher risk.
Bloody diarrhoea that comes on suddenly and severely is always an emergency. Contact your vet immediately.11 Parvovirus
Parvovirus causes severe, often bloody diarrhoea alongside vomiting and rapid deterioration. It's highly contagious, spreads easily in the environment, and can be fatal without prompt treatment. UK vaccination programmes protect against it.
An unvaccinated puppy with diarrhoea and vomiting is a potential emergency. Call your vet immediately.
Chronic or recurring diarrhoea: If your dog's diarrhoea keeps returning over weeks or months, or is accompanied by weight loss or a decline in condition, this needs full veterinary investigation. Conditions including IBD, liver disease, kidney disease, and certain cancers can all cause ongoing gastrointestinal symptoms.
What to Note Before Calling Your Vet
Having these details ready makes the call quicker and helps your vet guide you more accurately:
- How long has the diarrhoea been going on?
- How frequently is your dog going — and is it producing anything each time?
- What does it look like? Watery, soft, mucus, or blood-tinged?
- Has your dog eaten anything unusual recently?
- Any other symptoms — vomiting, lethargy, reduced appetite, or weight loss?
- Is your dog still drinking normally?
- Are vaccinations up to date? (Particularly important for puppies.)
- Has your dog recently started any new medication or food?
Call Your Vet Immediately
- There is blood in the diarrhoea — especially large amounts or a dark/tarry appearance
- You suspect AHDS (sudden onset, severe, bloody diarrhoea)
- Your dog is a puppy and not fully vaccinated (possible parvovirus)
- Diarrhoea is occurring alongside persistent vomiting — dehydration risk
- Your dog is collapsed, extremely weak, or clearly in pain
- You suspect poisoning or ingestion of something toxic
- Your dog is very young, very old, or has an existing health condition
These situations can deteriorate quickly. Do not wait — call your vet or emergency veterinary service straight away.
When to Contact Your Vet
- Diarrhoea hasn't settled within 24 to 48 hours in an otherwise well adult dog
- Your dog is off its food or refusing to drink
- There is any mucus in the stool, or it keeps changing in appearance
- Your dog seems lethargic or generally out of sorts
- Episodes are recurring — even if each one seems mild
- Your dog is losing weight alongside digestive symptoms
- You're unsure about the cause or you're worried
How Pet Med Direct Can Help
Pet Med Direct stocks a range of dog health products in the UK, including products for digestive support and parasite prevention. Some are available without a prescription; others require a valid prescription from your vet.
If your vet has recommended a specific product, browse the Pet Med Direct shop to see if it's available, and follow all instructions on the product label.
Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.
Frequently Asked Questions
My dog had one bout of diarrhoea but seems completely fine. Do I need to call the vet?
A single episode in an otherwise alert, active adult dog with no blood, no vomiting, and no signs of illness isn't always an immediate cause for concern. Monitor closely. If it happens again, if your dog seems unwell, or if you're in any doubt, contact your vet. Puppies and elderly dogs should be assessed sooner.
Is plain boiled chicken and rice safe for a dog with an upset stomach?
Many vets suggest a short period on a bland, easily digestible diet for mild cases of diarrhoea in adult dogs. However, you should always check with your own vet first, particularly if your dog has any existing health conditions, is on prescription food, or the diarrhoea seems more than mild. Don't use this approach for puppies without veterinary guidance.
Can dogs catch stomach bugs from people?
Some bacterial infections — such as Campylobacter — can potentially transfer between dogs and humans, though this is not the same as catching a stomach bug in the way people typically think of it. If your dog has diarrhoea and members of the household are also unwell, mention it to both your vet and your GP.
What does blood in my dog's stool mean?
Bright red blood in the stool (haematochezia) usually indicates bleeding in the lower digestive tract; dark, tarry stools (melaena) suggest bleeding higher up. Both need veterinary assessment. Sudden, severe, bloody diarrhoea — particularly if it looks like raspberry jam in consistency — should be treated as an emergency.
Why does my dog get diarrhoea when stressed?
The gut and the nervous system are closely connected. Stress hormones can speed up gut motility, leading to loose stools or diarrhoea. This is well-recognised in dogs and often linked to situations like travel, vet visits, fireworks, or changes at home. If it's a regular problem, your vet can help identify the triggers and discuss management options.
What is Giardia, and could my dog have it?
Giardia is a microscopic parasite that lives in the gut and is picked up from contaminated water or soil. It's relatively common in UK dogs and causes intermittent soft or watery stools, sometimes with mucus. It doesn't always cause obvious illness, which is why recurring mild diarrhoea is worth investigating. Giardia requires specific testing and treatment from your vet — standard worming products don't treat it.
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This this article is for informational purposes only and does not constitute veterinary advice.
If you are concerned with your dog’s health, please consult a qualified veterinarian.
If you are concerned with your dog’s health, please consult a qualified veterinarian.