Loose stool can be a minor event or a serious condition. Diarrhea can be acute (meaning that it begins rather suddenly and lasts more than 48 hours) or chronic (lasting more than three weeks, sometimes varying in intensity from day to day). Sometimes the reason for it is obvious, but often the exact cause can be surprisingly difficult to identify. Here are some of the most common causes of diarrhea in dogs.

In any case of digestive upset, it makes sense to look first at what your dog has been eating. A sudden change in your dog’s diet (for example, switching to a new food without a gradual transition period) can cause diarrhea. A food intolerance or food allergy is another possibility.

Dogs also have a well-known fondness for eating things that don’t belong to their intended diet. Dogs are scavengers, so it’s not unusual for them to consume “prizes” (like animal carcasses, garbage, and table scraps) that can lead to digestive upset. Diarrhea is an adaptation that helps scavenging animals get rid of the toxins and pathogens such material can contain. Getting into the human snacks or snarfing down a dead squirrel—an event more politely called a “dietary indiscretion”—is a very common cause of acute diarrhea in dogs.

In many of these cases, the diarrhea will resolve itself in a day or two. But if you believe your dog has eaten something poisonous (including chocolate), see your veterinarian immediately.

Go straight to the veterinarian if you think your dog has ingested a toy or any other object. Such foreign bodies are another possible cause of diarrhea. Materials that your dog’s body can’t digest have the potential to create a blockage in the gastrointestinal (GI) tract, interfering with the motility (movement) of the digestive system. As a result, the tissues near the obstruction may stretch and become inflamed, allowing liquid stool to seep around the blockage. Rawhide chews can sometimes also cause blockages, particularly if your dog swallows them whole instead of chewing them sufficiently.

Stress is another common reason for dogs to develop sudden diarrhea. In both humans and dogs, the body reacts to stress by releasing hormones and other chemicals that can disrupt the gut microbiome, the community of bacteria and other microorganisms that live in the GI tract. The stress trigger for a dog could be fireworks, dehydration, or an injury. A dog who has been hit by a car, for example, will often display signs of shock that include diarrhea.

Exercise-related diarrhea is very common in dogs, but it’s typically a short-term effect and not abnormal. The mechanisms are the same as in a human athlete: when the muscles are working hard, the body sends more blood flow to the muscles, directing it away from other areas, like the digestive system. The result can be a reduction of up to 80% in the blood flow going to the tissues of the GI tract, which changes the permeability of the intestinal walls. That redistribution of blood flow also raises the core body temperature and produces fluctuations in certain hormones. All of these changes can contribute to acute diarrhea.

Exercising in hot weather is sometimes a sufficient cause in itself, since diarrhea and nausea are common reactions to overheating.

Intestinal parasites—such as Giardia, tapeworms, hookworms, roundworms, and whipworms—are well-known to cause diarrhea in dogs. So are pathogens like the bacteria Clostridioides difficile (C. diff), Clostridium perfringens, Salmonella enterica, some strains of Escherichia coli (E. coli), and Campylobacter species.

You won’t be able to see bacterial pathogens, but some parasites may show up as white specks or grains in your dog’s stool. Take a poop sample to your veterinarian for parasite and pathogen screening. Keeping up-to-date with your dog’s monthly antiparasitic treatments is a good practice for preventing diarrhea.

If your dog’s diarrhea lasts for more than three weeks (either continuously or intermittently), and especially if bouts of diarrhea are accompanied by vomiting and loss of appetite, the culprit could be chronic inflammation in the GI tract. In this condition, called inflammatory bowel disease (IBD)—also known as chronic enteropathy (CE)—inflammation of the lining of the digestive tract interferes with its ability to process food and absorb nutrients.

IBD is also associated with disruption of the gut microbiome, with some bacterial populations growing too large and taking resources away from “good” bacteria. This imbalance or dysbiosis in the gut is associated with a reduction or loss of the beneficial bacteria it needs to function effectively.

Though the exact causes of IBD in any given case can be difficult to figure out, several potential treatments are available. According to the Merck Veterinary Manual, more than 50% of dogs with IBD respond to a diet change alone. And the bacterial imbalances in the gut microbiome associated with IBD can often be corrected by fecal microbiota transplant (FMT), which can be done with oral FMT capsules, such as DoggyBiome™ Gut Restore Supplement.

Some medications can cause diarrhea as a side effect. Antibiotics are one such example, which are used to treat bacterial infections. Unfortunately other bacteria in your dog’s gut can also be killed by antibiotics, thus disrupting the balance and diversity of your dog’s gut flora. Antibiotic-associated diarrhea can be reduced, and even prevented with taking the probiotic yeast, S. boulardii, one of the main ingredients in DoggyBiome’s S. boulardii + FOS supplement.

Sometimes diarrhea isn’t a result of something going on in the GI tract itself. Bacterial infections as well as viral infections —such as the canine parvovirus (parvo)—can lead to diarrhea. So can hormonal imbalances and even some cancers. Diarrhea may point to acute disease of the liver, pancreas, or kidneys. That’s why veterinarians typically suggest blood work when trying to diagnose a case of diarrhea.

Large intestine diarrhea tends to involve more frequent bowel movements. The stool is semi-formed and may contain mucus or flecks of red blood. Urgency—sometimes leading to “accidents”—is a typical characteristic of large intestine diarrhea. You might notice your dog straining, looking painful, or trying repeatedly to poop without producing much. If the individual stool piles or puddles produced are smaller than your dog’s usual poops (even if they’re more frequent), the large intestine is probably the origin of the diarrhea.

With small intestine diarrhea, the stool piles or puddles are typically larger than normal. That’s because inflammation in the small intestine interferes with that organ’s ability to absorb nutrients. Particles that would normally be absorbed by the small intestine instead pass on into the large intestine, pulling water along with them and creating a larger volume of poop.

Small intestine diarrhea tends to be less frequent, with no urgency and usually no visible blood. But because the small intestine is where most of your dog’s nutrients get absorbed, problems here can mean the body is missing out on a lot of the nutrition in your dog’s food. Small intestine diarrhea is more likely to be accompanied by vomiting, nutrient deficiencies, and weight loss. If blood is present, it is dark and tarry because it has been digested, unlike the fresh blood found in large intestine diarrhea.

Your dog’s poop can provide a lot of useful clues. What’s “normal” will depend in part on diet, age, and other factors, but in general, a healthy dog’s poop should be medium brown in color and should not be too hard or too soft.

Seek veterinary care immediately if your dog’s diarrhea is accompanied by any of the following factors:

• Lethargy
• Loss of appetite
• Bloating
• Apparent abdominal pain 
• Repeated vomiting
• Unproductive retching
• Large amounts of blood in the stool
• Ingestion of rat poison (or any other poison)

Eating a toy, glove, bag, or any other foreign object should also be treated as an emergency, since obstruction of your dog’s GI tract may require prompt surgical intervention.

In an adult dog, if diarrhea is the only symptom, you can wait a couple of days to see whether the episodes of diarrhea will resolve on its own. But seek veterinary attention if the diarrhea persists for more than three days, since it may indicate an underlying health condition.

Take along a fresh sample of your dog’s poop so that your veterinarian can test it for parasites and pathogens. Veterinarians tell us that about 50% of the time, such tests can identify potential causes of chronic diarrhea.

If the screening is negative for parasites and pathogens, your veterinarian may suggest a dietary trial to test whether the diarrhea is related to a food sensitivity. An elimination diet is the gold standard for identifying which foods are acting as triggers.

While many pet parents hope that food allergy testing will provide answers, research published in the Journal of the American Veterinary Medical Association has shown that many blood and saliva tests for allergies have a high false positive rate, and additional studies have also found such tests to be unreliable for identifying food allergies.

Occasional “normal” diarrhea often resolves itself in a day or two, but you may be able to help your dog feel better faster with one or more home remedies. If you’ve determined that your dog’s diarrhea isn’t an emergency, and it isn’t accompanied by any other symptoms, here are some tips for stopping it safely on your own.

Gut microbiome testing can tell you a lot about what’s going on in your dog’s digestive system and even how to correct certain problems. By identifying all the different kinds of bacteria in your dog’s gut, microbiome testing can determine whether those different bacterial populations are present in appropriate, balanced amounts when compared to the gut bacteria of healthy dogs. Those correct proportions are the key to a thriving, well-balanced microbiome.

The latest report for DoggyBiome’s Gut Health Test contains modules that offer targeted detection of specific pathogens and beneficial bacteria in dogs. This helps dog parents get to the root cause of their dog’s diarrhea symptoms and track specific pathogens overtime.

Bacteria belonging to the genus Escherichia (a group that includes E. coli), for example, are beneficial members of the community when they make up less than 5% of a dog’s gut microbiome. But an overgrowth of Escherichia can cause diarrhea and other digestive issues. And it turns out that 1 in 3 dogs have too much E. coli in their gut.

Bacteriophages (viruses that infect and kill certain strains of bacteria) that specifically target pathogenic strains of E. coli (such as PreforPro®) can help to bring the digestive tract into better balance. The journal Antibiotics has reported that such bacteriophages provide an effective alternative to antibiotic use in medical practice. Our DoggyBiome Gut Defender and DoggyBiome Oral Cleanse Powder both contain PreforPro® and are specifically formulated to reduce populations of E. coli in the mouth and upper digestive tract.

The Fusobacterium genus is also present in most healthy dogs. When these bacteria are missing, digestion can suffer, but high levels of Fusobacterium are also associated with digestive issues, particularly diarrhea, so moderation is key. Bacteria in the Fusobacterium genus do best in protein-rich environments, so if your dog’s Gut Health Test shows a deficiency in this kind of bacteria, increasing the protein content of their diet may help.

If the test shows that Fusobacterium levels are too high, the addition of a small amount of prebiotic fiber (like inulin) to the diet can help bring these levels down by supporting bacteria in the gut that make molecules that help fight inflammation.

A Gut Health Test can even offer clues about the underlying reason for a dog’s diarrhea. Low levels of Coprococcus and Oscillospira bacteria in the gut, for example, are often observed in dogs with food allergies. Deficiencies in Faecalibacterium have been associated with IBD in dogs.