Diarrhea/Runny Stools in Dogs: Why Is My Dog’s Poop Runny?

My dog has diarrhea. What caused it, and what do I do?

Diarrhea/Runny Stools in Dogs: Why Is My Dog's Poop Runny?

Diarrhea is a medical term describing unformed, loose stools. Bowel movements can be larger or more frequent. The poop might contain mucus, blood, worms, and all sorts of other things.

Who am I kidding–we all know what diarrhea is.

The important question is what caused it and what to do about it.

Stopping it is likely the first thing that comes to your mind. But while sometimes diarrhea develops for a straightforward reason, such as a dietary indiscretion, it can also be a symptom of a more complicated situation. In these cases, treating the symptom will not do anything to fix the real problem.

What causes diarrhea/runny stools in dogs?

Technically, your dog will have loose poop when things move through the system faster than they should. At the same time, the gut absorbs less water [and nutrients]. But what makes that happen? Brace yourself; the list is long.

Did you know that diarrhea doesn’t even have to be caused by problems originating in the gut itself?

Focus too much on diarrhea, and you’ll miss what’s really going on. You want diarrhea to stop, but you need to treat the cause to do that effectively.

Consider the big picture

How bad is the diarrhea? Is there also vomiting? Is the dog lethargic? Not interested in food? Does the dog look or act sick?

The longer your list of signs, the faster you should seek veterinary attention.

Note: A sick puppy is always an emergency. Don’t put your puppy’s life at risk by trying to treat them at home without first having them examined by a veterinarian.

Think back

Did your dog get into something they shouldn’t? Eat something unusual or suspicious? Did you start a new food or medication? Have there been any significant changes in your dog’s life? Even if they have not had access or gotten into anything, it is possible to have a tainted piece of food in the bowl.

An abrupt change in food, food items your dog isn’t used to, garbage gut, or even stress, excitement, and strenuous exercise can result in diarrhea.

When JD got diarrhea, we definitely had a suspect. While on a walk, he snatched and ate part of an unidentified carcass. Because we did have a suspect, and he looked normal otherwise, we decided to try a 24-hour fast,  followed by bland meals, to see whether his gut would settle down. It did.

Acute diarrhea from a dietary indiscretion should start to improve within 24 hours.

JD’s did last 48 hours, but we decided to wait another day because it was not an emergency, and it was on the weekend when the vet was closed. We would have taken him in if it hadn’t been resolved by then. Also, if his overall condition had worsened (he started vomiting or looking sick), we would have taken him in.

On the other hand, on the day Cookie clearly didn’t feel well, we would have taken her in if she had just one episode of diarrhea.

Severe, explosive, unrelenting diarrhea is an emergency.

Stool with blood in it calls for medical attention. Digested blood makes the feces appear black and tarry. In contrast, blood from lower in the gastrointestinal tract will appear bright red.

If your dog continues to have diarrhea for longer than a day or two, you need to see a vet. I would not wait any longer than that.

Just once, we waited longer, only to regret it. With her IBD, Jasmine had diarrhea fairly often. She was typically put on metronidazole, an antibiotic that also decreases inflammation in the gut. Now and then, Jasmine’s diarrhea would resolve on its own. Hoping it might do that and try to avoid yet another course of antibiotics, we decided to wait a second day to see if things improve. By the end of the day, she had blood in her diarrhea.

Large or small intestinal diarrhea?

Small intestinal diarrhea tends to be the worse of the two. The main job of the small intestine is digestion and nutrient and fluid absorption. When it’s not working properly, it not only results in diarrhea, but dogs may also not be getting the nutrition they need. This can lead to a dog who feels unwell and may quickly lose weight.

Common causes of small intestinal diarrhea can be quite scary, including parvovirus. Other possibilities include other viral infections, parasites, bacterial or fungal infections, poisoning, an abrupt deficiency in glucocorticoids (Addison’s disease),  pancreatic disease, garbage gut, inflammatory bowel disease, cancers, systemic disease (e.g., liver or kidney failure), and hemorrhagic gastroenteritis.

With small intestinal diarrhea, your dog might not have to go more than two to four times a day, but they will produce vast amounts of very wet stool. If there is blood in the stool, it will be dark, digested blood. With ongoing small intestinal diarrhea, your dog can start losing weight.

A dog with acute large intestinal diarrhea will need to go frequently, usually in a hurry. He is likely to strain while defecating and pass a smaller volume of feces at a time. There can be fresh blood or mucus in the stool. There is no loss of nutrients, and a dog with ongoing lower intestinal diarrhea will generally not lose weight.

Large intestinal diarrhea can be caused by parasites, inflammatory bowel disease, irritable bowel syndrome, cancer, bacteria, fungal infections, garbage gut, and other dietary issues.

When dogs have conditions that affect both the large and small intestines, a combination of symptoms can be seen.

When to see a vet

Diarrhea is such a common problem that most people want to treat it on their own. After all, we don’t see the doctor every time we get diarrhea. Many home remedies, such as a 24-hour fast, bland food, and adding fiber or probiotics to the diet, can be helpful.

If the cause is a garbage gut, your dog’s diarrhea might resolve on its own once the offensive matter leaves the system. However, you should see a vet when the stool doesn’t improve after 24 hours or if there are any other symptoms.

Trying to treat diarrhea without understanding the cause behind it is often counterproductive and can be dangerous.

What can cause diarrhea?

The cause behind your dog’s diarrhea can be simple or not.

  • dietary indiscretion
  • diet change
  • foreign body/obstruction
  • a food allergy or intolerance
  • intestinal parasites
  • bacterial infections
  • viral infections
  • fungal infections
  • toxins
  • pancreatic disease
  • immune-mediated
  • liver disease
  • kidney disease
  • cancer
  • Addison’s disease

Do you still feel confident that you can always deal with your dog’s diarrhea on your own? Unfortunately, the above is not a complete list!

If runny stools are the only sign and your dog is acting their normal self otherwise, you can see if they improve in a day or two with dietary management. However, if there are other symptoms in the mix, don’t wait.

Accompanying symptoms calling a vet visit include:

  • vomiting
  • loss of appetite
  • weakness
  • lethargy
  • abdominal pain

Symptoms that indicate your dog needs emergency medical attention include:

  • explosive watery diarrhea
  • diarrhea that doesn’t stop
  • profuse vomiting
  • weird-colored stool
  • bloody diarrhea
  • black tarry diarrhea
  • dark red or pale gums
  • sticky gums
  • marked weakness or lethargy

Chronic diarrhea

It can get confusing when your dog’s diarrhea comes and goes. It looks like it resolved, and then it comes back. It’s not really that bad; it just keeps happening. What to do then?

If the reason for your dog’s loose stools resolved, so would the loose stools. Even if the diarrhea isn’t all that runny and watery, I still urge you to see a veterinarian. While not an emergency, chronic or off-and-on diarrhea still tells you something important.


Diarrhea is a common problem dogs can have. The reason behind it can be simple or life-threatening. Instead of looking at it as a mere nuisance–which it certainly can be–keep in mind that it is an essential clue to what is happening with your dog’s health.

Take a cue from your dog. If a few runny bowel movements don’t seem to slow them down, it might be a self-limiting issue. If your dog does look and act ill, however, seek veterinary help.

Related articles:
A Tale of Many Tails—and What Came Out From Underneath 
Acute Small Intestinal Diarrhea
Acute Large Intestinal Diarrhea (Acute Colitis)
Chronic Large Intestinal Diarrhea
Chronic Small Intestinal Diarrhea

Further reading:
Diarrhea in Dogs

Categories: DiarrheaSymptoms

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Jana Rade edited by Dr. Joanna Paul BSc BVSc

I am a graphic designer, dog health advocate, writer, and author. Jasmine, the Rottweiler of my life, was the largest female from her litter. We thought we were getting a healthy dog. Getting a puppy from a backyard breeder was our first mistake. Countless veterinary visits without a diagnosis or useful treatment later, I realized that I had to take Jasmine's health care in my own hands. I learned the hard way that merely seeing a vet is not always enough. There is more to finding a good vet than finding the closest clinic down the street. And, sadly, there is more to advocating for your dog's health than visiting a veterinarian. It should be enough, but it often is not. With Jasmine, it took five years to get a diagnosis. Unfortunately, other problems had snowballed for that in the meantime. Jasmine's health challenges became a crash course in understanding dog health issues and how to go about getting a proper diagnosis and treatment. I had to learn, and I had to learn fast. Helping others through my challenges and experience has become my mission and Jasmine's legacy. I now try to help people how to recognize and understand signs of illness in their dogs, how to work with their veterinarian, and when to seek a second opinion. My goal is to save others the steep curve of having to learn things the hard way as I did. That is the mission behind my blog and behind my writing. That is why I wrote Symptoms to Watch for in Your Dog, which has turned out being an award-winning guide to dog owners. What I'm trying to share encompasses 20 years of experience. Dr. Joanna Paul BSc BVSc is our wonderful sponsor and has been kind to edit and fact-check my important articles.

  1. There can be so many reasons for dogs having the runs! Personally, I wouldn’t wait more than 2 days before seeing the Vet. You just never know what can be causing it.

  2. Thank you for a comprehensive post that will be an absolute life saver when people panic about their pups. Many people don’t know the finer details that make all the difference and THIS can matter. Being informed means you can take the right kind of action.

  3. I’m glad this is an issue I haven’t had to deal with for awhile! I think it’s something every dog owner will have to deal with, though, sooner or later. Very informative post.

  4. Really informative! I have a neighbor who lets her two Akita dogs run loose in the neighborhood. They will generally poop on my property. I’m always worried, my dog, Henry will find one of their droppings before I do and sniff it. Unfortunately, the Akitas don’t appear well. I’ve talked to the neighbors without much success. Their poop appears like chocolate pudding (very dark and very loose). When I had Henry at the vet a few weeks ago, the vet was alarmed and did a parasite test on him just to make sure he was healthy. I wish there was a way to make people be responsible pet owners. I feel bad for these Akitas and mad as hell at the neighbors. Besides the whole issue of them running loose, they aren’t healthy, nor do they even care. It’s maddening!

  5. Really interesting read and I have a vet document what to do when Layla has an upset tummy from my vet with all the instructions for emergencies

  6. This is a great resource to help people figure out what to do when their dogs have diarrhea.

  7. How quickly I react depends on who is having the issue. Shadow has IBS and he is super prone to diarrhea. The other cats I react faster because it’s more indicative of a problem.

  8. My cocker spaniel, Chipper often had diarrhea. And of course having two dogs, then I had to figure out which one had the problem. I found that giving a probiotic at the first hint of runny stools often helped. If I let it go too long, then the probiotics didn’t help and we had to see the vet for stronger ones.
    Very informative post. I didn’t know the difference between small and large intestine diarrhea.

    • Yeah, figuring out who left the runny poop or puke can be tricky with more than one dog if you’re not watching them every minute of the day.

      I’m glad that probiotics helped when used soon enough. The beneficial bugs keep bad bugs in check as well as contribute to nutrient conversion and gut health.

  9. Marjorie Dawson

    It is a good barometer of your dog’s health isn’t it? A bit of trouble might not mean too much but persistent issues should cause alarm bells to ring and a visit to the vet scheduled quickly.

    • I think the word barometer is the perfect way to describe it. Every other health problem, if not more, comes with diarrhea. Doesn’t help much with guessing what it might be but does help knowing that something isn’t right.

  10. Nancy Taylor

    Appreciate you distinguishing the truly alarming signs and when to visit the vet. We tend err on side of a vet appointment, so it’s good to know the red flags.

  11. It’s amazing how many things can cause loose stools. Such an important reminder not to just focus on stopping the diarrhea. It’s a shame our pets can’t tell us more about how they feel.

    • Yes, diarrhea is one of the most ambiguous symptoms. It may not even have anything to do with the digestive system directly at all. Focusing on treating it without getting to the bottom of it isn’t very helpful.

  12. It’s amazing what our pets’ stool can tell us about them. Toward the end of my cat, Cinco’s, life, he started getting diarrhea. I thought that maybe he just got into something that he shouldn’t have. As it turned out, he had stage 4 Lymphoma and I never knew it. It is definitely worth taking your pet to the veterinarian whenever diarrhea doesn’t resolve right away.

    • So sorry about Cinco. A diarrhea from just “getting into something” should go away within 24-48 hours. If it doesn’t, it’s something more than a dietary indiscretion.

  13. True pet parents obsess over their dogs poop! 🤣 I like how you separate out the difference and meaning of the large and small intestine indicators – super important!

    • Yes, where the diarrhea originates is quite telling in terms of the potential reason.

      The poop talk–can’t talk about dogs without ending up talking about poop. LOL

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