Dog Diarrhoea: The Complete UK Guide

Few things send a pet parent into a spin quite like discovering a puddle of runny mess where a healthy poo should be. If you're staring at the aftermath and wondering what on earth is going on with your dog, you're not alone. Diarrhoea in dogs is one of the most common reasons dog owners ring their vet, and the good news is that most bouts are mild and pass quickly.

In this complete UK guide, we'll walk through what diarrhoea actually is, the most common causes of diarrhoea in dogs, the signs and symptoms to watch for, when to contact your vet, and how to care for your furry friend at home. By the end, you'll feel far more confident about what's normal, what's not, and what to do next.

What is diarrhoea?

Diarrhoea simply means loose stools that are watery or unformed and passed more frequently than usual. It happens when something disrupts the normal workings of your dog's digestive system — food moves through the intestines too quickly, or the gut struggles to absorb water and nutrients properly. You may notice soft stools one day and fully unformed stools the next as things settle.

Your dog's digestive tract is a clever piece of kit. Food travels from the stomach into the small intestine, where most digestion and nutrient absorption happens, then into the large intestine (the colon), where water is reclaimed and firm stools are formed. When any part of that journey through the GI tract is thrown off, the result is diarrhoea. Understanding stool consistency is one of the simplest ways to read what's happening inside your canine companion.

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Signs and symptoms of diarrhoea

The most obvious clue is a change in your dog's bowel movements — but diarrhoea rarely travels alone. Here are the signs and symptoms worth keeping an eye on.

Mild diarrhoea in an otherwise well dog — one that's still bright, eating and acting normal — is usually nothing to panic about. It's when these clinical signs cluster together that you should pay closer attention. Persistent vomiting and diarrhoea, a dog that's lethargic, or a clear loss of appetite all point to something needing a closer look.

What causes diarrhoea in dogs?

There's a long list of possible triggers, ranging from a cheeky raid on the bin to a more serious underlying condition. The causes of diarrhoea span everyday tummy upsets and more serious illness, so let's start with the everyday culprits before working up to the ones that need veterinary attention.

Common causes of diarrhoea in dogs

These are the most common causes you'll come across as a dog owner — and thankfully, many are minor.

• Dietary indiscretion: This is the number-one cause — your dog eating something they shouldn't. Table scraps, spoiled food, a bin raid, or a snack of garbage in the park all count as dietary indiscretion, and the result is often a swift upset tummy.
• A sudden change in diet: A change in diet done too quickly is a classic trigger. Switching foods overnight, or introducing a new food without transitioning gradually, upsets the gut microbiome and the healthy gut bacteria that keep digestion running smoothly.
• Stress or anxiety: Yes, nerves can cause the runs. Stress-induced diarrhoea is common after kennel stays, house moves, fireworks or separation anxiety. Emotional stress and anxiety genuinely affect gut health.

Food allergies and intolerances

Sometimes the trouble isn't a one-off snack but the everyday menu itself.

• Food allergies: A true food allergy is an immune response to a particular protein, and food allergies often show up as recurring loose stool alongside itchy skin or ear trouble.
• Food intolerance and sensitivity: A food intolerance or food sensitivity is different — the gut simply struggles to digest a certain ingredient, leading to soft stool or a grumbly tummy. An elimination diet, guided by your vet, is the usual way to pin it down.

Parasites and worms

Bugs of all kinds can inflame the gastrointestinal tract and cause diarrhoea in dogs.

• Intestinal parasites: Internal parasites such as roundworms, hookworms and whipworms are frequent offenders, along with coccidia and giardia. Roundworms, hookworms, whipworms and coccidia are all worms and single-celled parasites that can inflame the gut, and these worms often need a faecal exam to diagnose. Giardia in particular is a common cause of loose stool in dogs that spend time around other animals.
• Bacterial and viral infections: Bacterial infections caused by salmonella, campylobacter or E coli can inflame the intestines. These bacterial infections often need a vet to confirm and treat. Viral infections are more serious — parvovirus (parvo), canine distemper and coronavirus can all cause severe, sometimes bloody diarrhoea, especially in unvaccinated puppies. A fungal infection is a rarer cause.

Toxins, foreign bodies and medications

• Toxins and poisons: Ingesting toxins or toxic foods such as chocolate and grapes can cause diarrhoea alongside other worrying signs. Never wait if you suspect your dog has eaten poisons.
• Foreign objects: The ingestion of foreign objects — socks, stones, toys — can lead to a partial or complete intestinal blockage. A gut blockage or obstruction caused by swallowed foreign objects is a genuine veterinary emergency.
• Medications: Some medications upset the stomach. Antibiotics can disturb gut bacteria, and NSAIDs (anti-inflammatory drugs) can irritate the digestive tract.

Underlying health conditions

Chronic or recurring diarrhoea can point to an underlying health issue that needs proper diagnosis.

• Digestive and organ disease: Colitis, inflammatory bowel disease (IBD), pancreatitis (inflammation of the pancreas), and exocrine pancreatic insufficiency (EPI) all disrupt digestion. Liver disease, kidney disease and other organ disease can too — both liver disease and kidney disease often reveal themselves through recurring tummy upsets, so they're worth ruling out.
• Inflammatory bowel disease and endocrine trouble: Inflammatory bowel disease is a long-term cause of chronic loose stools, while hyperthyroidism and other endocrine disease can affect stool too. More rarely, intestinal cancer or a tumour is the underlying cause.
• Gastroenteritis and HGE: Gastroenteritis (inflammation of the stomach and intestines) is common, while haemorrhagic gastroenteritis (HGE) causes sudden, dramatic watery diarrhoea with blood and needs urgent care.

Types of diarrhoea in dogs

Vets often categorise diarrhoea by where in the gut it originates and how long it lasts. Knowing the type helps pinpoint the underlying cause.

Small intestinal diarrhoea

Small intestinal diarrhoea (or small bowel diarrhoea) tends to produce large volumes of watery diarrhoea, sometimes with weight loss and flatulence, because the small intestine struggles to absorb nutrients. Straining is usually minimal.

Large intestinal diarrhoea

Large intestinal diarrhoea (large bowel diarrhoea) comes from the colon. You'll typically see small, frequent amounts of stool, straining to defecate, and often blood and mucus. This large intestinal diarrhoea is the type most linked to colitis.

Acute and chronic diarrhoea

Acute diarrhoea comes on suddenly and often clears up quickly — many mild cases are self-limiting and resolve on their own within a day or two. Chronic diarrhoea is defined as lasting more than three weeks (or coming and going), and always warrants a diagnostic workup. Acute diarrhoea from a dietary slip-up is very different from chronic diarrhoea caused by IBD, so the distinction matters.

Puppy diarrhoea

Puppy diarrhoea deserves special mention. Puppies — and especially young puppies — are far more vulnerable to dehydration than adult dogs, and they can go downhill frighteningly fast. Because puppies may not be fully vaccinated, diarrhoea can be a sign of parvovirus, which is life-threatening.

The same caution applies to any dog that is very young or very old, or one with a compromised immune system. If you have a puppy or a senior dog with diarrhoea, don't take the "wait and see" approach you might with a healthy adult — contact your vet promptly. For more on feeding little ones, see our guide on when to switch a puppy to adult dog food.

How serious is diarrhoea in dogs?

Most of the time, not very. One episode of diarrhoea in a dog that is otherwise well, still eating and acting normal, will often settle without any drama. The trouble is that diarrhoea can also be the first clinical sign of something more serious, which is why the surrounding symptoms matter so much.

The biggest immediate risk is dehydration. Every watery poo drains fluids and electrolytes, and in severe cases this becomes dangerous quickly. Some causes, like parvo and HGE, are genuine veterinary emergencies. And remember that certain causes — such as giardia and salmonella — can be contagious to other pets and even people, so good hygiene matters.

Don't ignore this

When to contact your vet

Knowing when to see the vet is the single most useful skill here. As a rule, one bout in a bright, happy dog can be monitored at home. But you should contact your vet if the diarrhoea lasts more than 24 hours, or if you see any of the red flags below.

When should I take my dog to the vet?

If your dog seems otherwise fine, monitoring for 24 hours is reasonable. But if diarrhoea persists beyond 48 hours, or you spot lethargy, low energy, a reduced appetite, weight loss, straining, or clear signs of dehydration, it's time for veterinary advice. Anything suggesting a blockage, poisoning or HGE is a veterinary emergency — call your vet or the nearest emergency animal hospital immediately rather than waiting.

At the clinic, your veterinarian may run a faecal exam, blood tests or imaging as part of a diagnostic workup to reach a diagnosis and identify any underlying condition. A good veterinarian will also check for hidden causes like food allergies or a foreign body when diarrhoea keeps coming back. Trust your instincts — you know your canine companion best, and no vet will ever mind you checking.

How to treat diarrhoea in dogs

For a healthy adult dog with mild diarrhoea and no other symptoms, simple supportive care at home is usually all that's needed. Never give human medicines or leftover antibiotics without veterinary advice — the right treatment always depends on the cause.

1. Consider a short fast

   For a healthy adult, a brief 12-24 hour fast (removing food, never water) lets the digestive system rest. Do not fast puppies, senior dogs or unwell dogs — remove food only on veterinary advice.

2. Keep fluids up

   Always leave plenty of fresh water available to replace lost fluids and electrolytes. Read our guide on how much water your dog should drink to know what's normal.

3. Reintroduce a bland diet

   Offer a bland diet that's easy to digest, such as boiled chicken and rice. Serve smaller meals, little and often, rather than one big bowl.

4. Return to normal food gradually

   Once stools firm up, mix the bland diet back into their usual food over a few days to avoid a fresh upset stomach.

What to feed a dog with diarrhoea

Chicken and rice is the classic choice, but dogs with sensitive stomachs may do better on a specially formulated sensitive food with high-quality protein and gentle fibre. A little plain, cooked pumpkin adds soluble fibre that can help firm things up.

Home remedies for dog diarrhoea

Alongside a bland diet, a few gentle home remedies can support recovery in mild cases.

• Probiotics and prebiotics: These help restore healthy gut bacteria and rebalance the gut microbiome after a tummy upset.
• Pumpkin: A spoonful of plain pumpkin is a well-loved, fibre-rich remedy for a mild stomach upset.
• Rest and calm: If stress or anxiety is the trigger, a quiet routine and comfort do wonders for gut health and can ease a leaky gut over time.

How do I look after my dog when it has diarrhoea?

Beyond diet, a few practical steps make life easier for both of you. Take your dog out more often to avoid accidents, and pop on a fresh poop bag ready — you'll be scooping more dog poop than usual. Clean up promptly and wash your hands well, as some causes are contagious.

Keep a note of each episode, the stool consistency, and any other symptoms so you can give your vet a clear picture. Frequent watery stools can also irritate the anal glands and leave a mess around the rear, so a gentle wipe-down keeps your pooch comfortable and less whiffy — you might find our post on why your dog smells bad handy too.

Quick questions

Remember, you know your dog better than anyone — when in doubt, a quick call to your vet is always worth it. Here's to happy tummies and tidy poos! Loved this guide? Explore more on our blog, including how often your dog should poop and why your dog might be pooping in the house.

Sources & further reading

• How Much Water Should My Dog Drink? — Tuff Pets
• How Often Should My Dog Poop? — Tuff Pets
• Feeding Your Dog at Different Life Stages — Tuff Pets