The most common reason dogs get diarrhea is eating something they shouldn’t have. Veterinarians call this “dietary indiscretion,” which covers everything from garbage and table scraps to rabbit droppings and foreign objects. But diarrhea can also signal infections, chronic disease, toxin exposure, or stress. Understanding what’s behind it helps you decide whether to ride it out at home or head to the vet.
Dietary Indiscretion: The Most Likely Culprit
Dogs are scavengers by nature, and their stomachs pay the price. Eating garbage, human food scraps, sticks, toys, or animal feces is the single most common trigger for digestive upset across all age groups. The resulting diarrhea is usually acute, meaning it comes on suddenly and resolves on its own. In most cases, diarrhea from dietary indiscretion improves within 48 hours with basic supportive care.
Certain human foods are especially problematic. Fatty or greasy foods can overwhelm your dog’s digestive system, and rich holiday meals are a classic trigger. Dairy products cause trouble for many dogs because they lack the enzymes to properly break down lactose. Sudden changes in dog food brands or formulas can also set off a bout of loose stool, even when the new food is perfectly fine on its own. The gut just needs time to adjust.
Parasites and Infections
Intestinal parasites are a frequent cause of diarrhea, particularly in puppies and dogs who spend time outdoors. Roundworms, hookworms, whipworms, giardia, and coccidia all colonize the digestive tract and disrupt normal function. Dogs pick up coccidia by swallowing eggs shed in contaminated feces or by eating prey animals like mice. Those eggs become infectious within hours of hitting the environment, which is why areas with multiple dogs (shelters, boarding facilities, dog parks) carry higher risk.
One frustrating aspect of parasitic infections is that your dog may already be sick before the parasites show up on a test. With coccidia, for example, dogs can develop diarrhea before they start shedding eggs in their stool, so a single negative fecal test doesn’t always rule it out. Repeat testing is sometimes needed. Vets typically use a centrifugal flotation method to detect parasites, which spins fecal samples in a centrifuge to separate parasite eggs from debris. It’s significantly more sensitive than older passive methods. For harder-to-detect organisms like giardia, antigen tests or PCR panels can confirm a diagnosis.
Bacterial and viral infections also cause diarrhea. Parvovirus is the most dangerous, particularly for unvaccinated puppies, and produces severe, often bloody diarrhea with vomiting and rapid dehydration. Bacterial infections from salmonella or campylobacter can hit dogs who eat raw meat or contaminated food.
Household Toxins and Chemicals
Your home contains more potential digestive irritants than you might expect. Liquid laundry detergent and detergent pods cause stomach upset and irritation to the mouth and throat. Dryer sheets and fabric softeners are worse: they contain compounds that can cause chemical burns to the mouth, esophagus, and stomach. Even cosmetics like lip gloss and moisturizing lotions can trigger diarrhea because ingredients like shea butter act as laxatives. Petroleum jelly works the same way.
Toothpaste deserves special caution. Small amounts cause mild stomach upset, but a large ingestion introduces enough fluoride to cause severe gastrointestinal distress along with dangerous changes in heart rhythm, blood pressure, and electrolytes. Vinegar, enzyme-based cleaners, and bar soap generally cause only mild upset, but the volume matters. If your dog got into any household product, the ASPCA Poison Control hotline can help you assess the risk.
Chronic Diarrhea and Underlying Disease
When diarrhea persists for weeks or keeps coming back, the cause is usually something deeper than a dietary mistake. Inflammatory bowel disease (IBD) is one of the more common chronic causes. It involves ongoing inflammation in the intestinal lining that interferes with nutrient absorption and produces recurring loose stools, sometimes with mucus or blood. Diagnosing IBD isn’t straightforward because the inflammation itself isn’t unique. Vets arrive at a diagnosis by first ruling out every other possible cause, including diet reactions, parasites, bacterial infections, and fungal agents. There’s growing evidence that gut bacteria play a central role in either triggering or sustaining the inflammation.
Exocrine pancreatic insufficiency (EPI) is another chronic condition where the pancreas doesn’t produce enough digestive enzymes. Dogs with EPI can’t properly break down food, so they develop chronic diarrhea, lose weight despite eating large amounts, and often produce pale, greasy-looking stool. German Shepherds and Rough-Coated Collies are genetically predisposed, but it can occur in any breed.
In older dogs, chronic diarrhea may also stem from kidney disease, liver problems, or certain cancers affecting the digestive tract. These conditions tend to come with other symptoms like weight loss, changes in thirst and urination, or a dull coat.
Stress and Anxiety
The gut-brain connection is real in dogs, just as it is in people. Boarding, travel, moving to a new home, the addition of a new pet or baby, loud events like thunderstorms or fireworks: all of these can trigger stress-related diarrhea. It typically resolves once the stressor passes and the dog settles back into routine. If your dog consistently develops loose stool during predictable events, that pattern itself is a useful clue.
Puppies vs. Senior Dogs
Age changes the risk profile significantly. Puppies are more vulnerable to infectious causes because their immune systems are still developing. Parvovirus is the biggest threat for unvaccinated or incompletely vaccinated puppies, but parasitic infections are also extremely common in young dogs. Puppies also explore the world with their mouths, making dietary indiscretion and toxin ingestion more likely.
Senior dogs are more prone to organ-related causes. As the kidneys, liver, and pancreas age, they become less efficient, and diarrhea can be an early sign of declining function. Older dogs are also more likely to develop tumors that affect the gastrointestinal tract. Any persistent change in stool quality in a senior dog warrants investigation, even if the dog seems otherwise fine.
How to Check for Dehydration at Home
Diarrhea pulls water out of your dog’s body quickly, and dehydration is the most immediate risk. You can do a simple skin turgor test at home: gently pull up the skin at the back of your dog’s neck or along the spine, then release it. In a well-hydrated dog, the skin snaps back to normal almost immediately. If it returns slowly or stays tented for a moment, your dog is likely dehydrated.
Test two or three locations for consistency, and keep in mind that this method has limitations. Overweight dogs may seem better hydrated than they are because extra fat under the skin increases elasticity. Older or very thin dogs may seem more dehydrated because their skin naturally has less snap. In very young puppies, the test is unreliable altogether due to the high water and fat content in their skin. Other signs of dehydration include dry or tacky gums, sunken eyes, and lethargy.
Managing Mild Diarrhea at Home
For an otherwise healthy adult dog with no other symptoms, a bland diet is the standard first step. The most common recipe is 75% boiled white rice mixed with 25% boiled lean protein, either skinless, boneless chicken breast or lean ground beef like sirloin. Keep portions small and feed more frequently than usual.
Once your dog’s stools return to normal and stay that way for at least 24 hours, begin transitioning back to regular food gradually. Mix increasing amounts of the normal diet with decreasing amounts of the bland diet over several days. A typical bland diet regimen lasts about 10 days total, though your dog’s response may shorten or lengthen that timeline. Adding a probiotic can help: studies on dogs fed probiotic-containing diets show a modest but statistically significant reduction in days with loose stools compared to dogs without probiotics.
Signs That Need Veterinary Attention
Not all diarrhea can wait out the 48-hour window. Seek veterinary care if your dog stops eating, becomes lethargic, or starts vomiting alongside the diarrhea. Black or tarry stool is a specific red flag because it indicates partially digested blood from higher in the digestive tract. Fresh red blood in the stool also warrants a visit. If a bland diet hasn’t improved things within two to three days, something more than a simple stomach upset is going on.
Puppies, senior dogs, and small breeds have less margin for error with dehydration, so the threshold for seeking help should be lower. A large adult dog with one or two episodes of loose stool and normal energy is a very different situation from a puppy with watery diarrhea who won’t eat.