Diarrhoea in Dogs: Causes, Warning Signs and When to Call the Vet

Diarrhoea in dogs means loose or watery stools, and it is one of the most common reasons dogs see a vet. A 2025 study of UK practice records by the Royal Veterinary College’s VetCompass programme found about 1 in 12 dogs were diagnosed with acute (sudden-onset) diarrhoea in a single year. Many cases are mild, but some are not, so speak to your vet if you are unsure.

At a glance

• What it is: loose or watery stools, with many possible causes.
• Who it affects: any dog, though the RVC study found higher odds in dogs under 3 and over 9.
• Urgency: soon, and as soon as possible if your dog seems unwell, has blood in the stool or it has lasted more than 24 hours.
• Vet needed? Usually, unless it is mild, lasts under 24 hours and your dog is otherwise well.

Signs to look for

Alongside the loose stools, the PDSA lists blood or mucus in the stool, severe or constant watery diarrhoea, eating less than usual, vomiting, low energy and a painful tummy. A painful stomach can show as yelping when you pick your dog up, or standing in a “prayer position” with front legs down and back end up.

In the VetCompass records, about 3 in 10 dogs had blood in the diarrhoea and just under half were also vomiting. If you are not sure whether your dog is eating enough, our guide on how to tell if your dog isn’t eating enough may help.

Causes and risk factors

The PDSA describes causes ranging from eating rich, fatty or unsuitable food, food allergy or a sudden diet change, to infections such as parvovirus, worms, giardia and bacteria such as Salmonella and Campylobacter. Bigger problems can also show up as diarrhoea, including a blockage from something swallowed, inflammatory bowel disease, pancreatitis and liver disease.

In the VetCompass study, the most common suspected explanations were scavenging or dietary indiscretion (9.5% of cases) and gastroenteritis (8.1%). Figo once scoffed something dodgy on a walk, so I know how easily that one happens. The Kennel Club adds stress, switching food too quickly and parasites.

Breed patterns exist too. Compared with crossbreeds, the PLOS One paper found higher odds in Maltese, Miniature Poodles, Cavapoos, German Shepherds and Yorkshire Terriers, and lower odds in Chihuahuas and Jack Russell Terriers. That describes patterns in records, not what will happen to your dog.

When to call your vet

The PDSA says a mild bout lasting under 24 hours in an otherwise well dog may be settled at home first, but if your dog seems unwell or has had symptoms for more than 24 hours, it is “always best to contact your vet for advice”. Speak to your vet sooner if your dog is very young or elderly, or is taking anti-inflammatory painkillers.

The Kennel Club lists blood, black and tarry stools, repeated vomiting, very frequent diarrhoea, tiredness, loss of appetite, signs of pain and fever as reasons to get advice, and says to take your dog to the vet as soon as possible if things do not improve or get worse. The PDSA describes parvovirus as causing very severe diarrhoea and vomiting, often with blood, which is another reason not to wait with a puppy. Our vets guide helps you find one, and sick dog symptoms covers wider warning signs.

How vets diagnose it

A vet will ask about the diet, what your dog could have eaten and how long it has lasted, then examine your dog. The PDSA says they may ask for a stool sample. In the VetCompass records, 82% of dogs had no laboratory tests at the first visit. Where tests were done, blood tests were the most common (11%), so what your vet suggests depends on how unwell your dog is.

What vets generally do about it

Treatment is decided by your vet. In the VetCompass study, the most common approaches were probiotics (about 60% of cases), dietary management (44%), antibiotics (38%) and anti-sickness medicine (24%), and 7% of dogs were hospitalised. The PDSA notes antibiotics are usually unnecessary because most cases are not bacterial, and the study’s authors flagged how often they were used. In the same VetCompass study, around 80% of cases needed only one visit to the vet for the episode.

Living with it and prevention

For a mild, short episode in a well dog, the PDSA advises keeping fresh water available, since dogs lose extra fluid, resting your dog and avoiding rich or fatty food. It also warns against carrying on with a homemade bland diet for more than a few days without checking with your vet, and advises against fasting very young, old or ill dogs.

For prevention, the Kennel Club recommends changing food slowly over 7 to 10 days. Our pet insurance guide is worth a read before you need it, and the full list of conditions is on our dog illnesses A to Z.

Related conditions

• Vomiting in dogs
• Gastroenteritis in dogs
• Parvovirus in dogs
• Giardia in dogs
• Worms in dogs
• Pancreatitis in dogs

Sources

• PDSA, Dog diarrhoea
• The Kennel Club, Dog diarrhoea
• O’Neill et al. (2025), PLOS One, Epidemiology and clinical management of acute diarrhoea in dogs under primary veterinary care in the UK
• Royal Veterinary College VetCompass, Diarrhoea infographic

This page is general information, not veterinary advice. If you are worried about your dog, speak to your vet. Written by Georgiana & Figo, who are dog owners, not vets. Have a look around Calmshops for everyday dog essentials.