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The Most Common Causes of Diarrhea in Dogs

Dog scavenging rubbish

Diarrhea 101

No one wants their dog to have diarrhea: it's unpleasant for the dog, damages the rug, and disturbs your sleep. Many dogs with dodgy tummies can be treated at home, but ideally the dog would avoid getting diarrhea in the first place. This may be possible when you know what some of the causes of diarrhea are—and there are more than you think. 

While simple changes (such as offering a different food) are all that's needed for some dogs, for others the diarrhea may be a clue to a wider health problem. But whatever the cause, it's vital that the dog sees a vet if they have other symptoms, pass blood, or seem unwell. 

9 common things that cause diarrhea

So, what causes diarrhea in dogs? There are a handful of common things.


There's a saying that goes "common things are common," and this is so true for parasites and diarrhea—especially in puppies. It's a good idea to regularly deworm your pet. But be aware that each dewormer acts against slightly different types of worms, so giving a treatment doesn't guarantee worms can be completely ruled out as a cause of diarrhea. 

Eating indiscriminately

The chow hound that dines off the sidewalk is a hazard to their own stomach. Scoffing down that cast-aside burger is a fast track to food poisoning. Another side of scavenging is that the foods are sometimes rich or fatty, which can also cause an upset tummy. So even if the dog avoids picking up an infection, they aren't out of the woods with regards to indiscriminate dining as one of the causes of dog diarrhea.

Sudden changes of diet

Digestion is complicated. It starts with a good quality food and proceeds with digestive juices in the stomach. As it passes down the gut, bacteria and digestive enzymes get to work. But be aware that certain types of bacteria work best with certain foods. A sudden change of diet can leave the gut under equipped for the job in hand, which means diarrhea!

This is easy to avoid when you switch foods slowly. Take several days mixing the old and the new together in increasing proportions until the swap is made. 

Food intolerance or allergy

Sometimes you can feed a great food, but it gives the dog diarrhea. This is no reflection on the quality of the diet, but rather an indication that the dog's gut can't cope with the food. A human example of this is a person with lactose intolerance. When they eat anything with milk in, no matter how delicious or healthy, it upsets their stomach. The same thing happens in dogs. 

There is a subtle difference between dietary intolerance (difficulty digesting the food) and allergy (which causes gut inflammation). Food intolerance can occur at any age, but can also affect older dogs as their gut ages. This means that a food they've eaten all their life with no problem now gives them a tummy upset.

On a different note, food allergy not only causes diarrhea, but for some dogs also causes intense itching. Something to bear in mind if this sounds like your best buddy. 

Poor diet and nutrition

What happens if you put diesel in a gas engine? Not a lot! Feed a dog a diet that's high in cheap fillers or hard-to-digest plant proteins such as soy, and things won't end well. Just as a vehicle can't run on the wrong fuel, the dog's gut will rebel and reject poor food in the form of diarrhea. 

Always feed a high-quality diet. Read the label and look for a food that lists named meats as the top three ingredients. The rest should read like a delicious restaurant menu, not a list of chemicals. Raw diets are also gaining popularity and can be a healthy alternative to carb-heavy kibbles.


We often think of infection as one of the main causes of dog diarrhea, but what you may not realize is just how many types of infectious agents are out there just waiting for your dog to pick up. These range from bugs commonly found in soil right through to some nasty viruses that can be life threatening. It's not always important to label the bug, because what matters most is recognizing when the dog is sick and needs to see the vet.  

An interesting group of infections that are on the rise include salmonella, E.coli, and campylobacter. These bugs are commonly found in low-quality or improperly kept raw meats and are capable of not only causing diarrhea in dogs, but also can be passed onto people. Don't believe the myth that dogs are resistant to salmonella—it simply isn't true!

Inflammatory bowel disease (IBD)

As the name suggests, IBD is a condition where the gut wall becomes inflamed and can't do its job properly. There are many factors that can trigger IBD, including a genetic trait, food allergy, or even stress. IBD is complicated to diagnose as there is no one test that gives a yes/no answer. The vet will need to rule out all other reasons behind diarrhea before they can say for sure the dog has IBD. 

Lack of digestive juices

Some dogs lack the digestive juices (or enzymes) necessary to digest their food. The German Shepherd is the poster-dog for this, with a condition called EPI (exocrine pancreatic insufficiency). Dogs with this condition struggle to digest fatty foods and produce a particularly unpleasant diarrhea. These are often young dogs that struggle to gain weight and grow poorly. The condition can be helped by giving a supplement that contains the missing pancreatic enzyme.

Complications from another disease

When looking at the things that cause diarrhea in dogs, remember that diarrhea is just a symptom. It's a clue that the gut isn't working well, but doesn't tell you anything about why this is so. For some dogs, their diarrhea is a complication of disease elsewhere in the body. For example, a dog with heart failure may have diarrhea because the gut wall is retaining fluid and can't absorb food. 

If your dog is unwell, thirsty, losing weight, has a poor appetite, or displays any other symptoms, then it's important to see the vet. Likewise, if the tummy upset goes on for longer than 24 hours, or the dog is elderly or a pup… visit the vet.

Learn more about diarrhea in dogs


The article was written by  Pippa Elliot, BVMS, MRCVS on October 24, 2020.

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