Why Is My Dog Having Diarrhea? Common Causes and What to Do
Diarrhea is one of the most frequently reported signs in dogs, and while it often resolves on its own, understanding what to look for can help you decide when veterinary care is needed.
Quick Answer
Diarrhea in dogs can be caused by dietary changes, food intolerance, infections, parasites, stress, or underlying conditions such as inflammatory bowel disease. Most mild cases resolve within a day or two, but diarrhea lasting longer than 48 hours, containing blood, or accompanied by vomiting or lethargy should be evaluated by a veterinarian.
SYMPTOM TRIAGE
Answer a few questions about your dog's signs and receive general guidance on how urgently to seek veterinary care.
This tool does not diagnose conditions or replace a veterinarian.
Common Causes of Diarrhea in Dogs
Dietary factors are among the most frequent explanations for diarrhea in dogs. A sudden change in food brand or formula, the introduction of a new treat, or access to table scraps can disrupt the digestive system and lead to loose stools. Some dogs have specific food intolerances or sensitivities to ingredients such as certain proteins, grains, or dairy products.
Infections are another common cause. Bacterial infections (including Salmonella, Campylobacter, or E. coli), viral infections (such as canine parvovirus or coronavirus), and protozoal infections (such as Giardia) can all produce diarrhea, often accompanied by other signs like vomiting, reduced appetite, or fever.
Intestinal parasites, including roundworms, hookworms, whipworms, and Giardia, are sometimes associated with diarrhea, particularly in younger dogs or dogs with incomplete deworming histories. Parasite-related diarrhea may contain visible mucus or worms in some cases.
Stress and anxiety can also affect a dog's digestive system. Changes in routine, travel, boarding, or a new pet or family member may trigger loose stools. This type of diarrhea is typically temporary and resolves once the stressor is removed or the dog adjusts.
Inflammatory bowel disease (IBD) is a chronic condition that can cause recurrent or persistent diarrhea. It is sometimes associated with weight loss, changes in appetite, and fluctuating stool quality over weeks or months. A veterinarian can assess whether IBD or another chronic gastrointestinal condition may be contributing.
Toxin exposure, such as ingesting spoiled food, compost, or chemicals, may also lead to sudden diarrhea, sometimes accompanied by vomiting.
What to Observe About Your Dog's Diarrhea
When your dog has diarrhea, paying attention to the stool and overall behavior can provide useful information. The following details are worth noting:
- Consistency: Whether the stool is soft, watery, or contains visible mucus or fat. Watery diarrhea increases the risk of dehydration.
- Color: Normal brown stool may turn yellow, green, black, or red. Black, tarry stool can sometimes indicate digested blood in the upper gastrointestinal tract, while red streaks or fresh blood may come from the lower tract.
- Frequency: How many episodes of diarrhea have occurred and whether there is any pattern.
- Presence of blood or mucus: Small amounts of mucus can be seen with intestinal irritation, but significant blood or large amounts of mucus warrant veterinary attention.
- Duration: Whether the diarrhea began recently or has been ongoing for days.
Alongside the stool, observe your dog's energy level, appetite, water intake, and whether they are showing abdominal discomfort, vomiting, or fever.
What to Monitor and When to Seek Veterinary Care
For a healthy adult dog with a single episode of mild diarrhea and no other signs, a short period of observation at home may be reasonable. Feeding a bland, easily digestible diet in small, frequent portions and ensuring access to fresh water can support recovery in some cases.
However, contact a veterinarian if any of the following apply:
- Diarrhea persists for more than 48 hours
- The stool contains blood or is black and tarry
- Your dog is also vomiting, refusing to eat or drink, or showing lethargy
- Your dog is a puppy, a senior, or has a known health condition
- There is a sudden onset of large-volume, watery diarrhea
- Your dog appears to be in pain, has a swollen or tense abdomen, or is straining without producing stool
- You suspect your dog has ingested a toxin or foreign object
When to Contact a Veterinarian
A veterinarian should be contacted promptly whenever diarrhea is severe, persistent, or accompanied by other concerning signs. Puppies are especially vulnerable to dehydration and the effects of infections such as parvovirus, so any diarrhea in a young dog that does not improve within 12 to 24 hours should be evaluated.
Your veterinarian can perform a physical examination, fecal testing, or other diagnostics to identify the underlying cause and recommend appropriate treatment, which may include dietary modification, deworming, or medications.
Frequently Asked Questions
Can certain dog foods cause diarrhea?
Yes, sudden changes in diet, new treats, or ingredients that a dog cannot tolerate well can all lead to diarrhea. Transitioning to a new food gradually over several days can help reduce the chance of digestive upset.
Is it normal for my dog to have diarrhea after boarding?
Some dogs develop loose stools during or after boarding due to stress or changes in routine and diet. If the diarrhea is mild, resolves within a day or two, and the dog otherwise seems well, it may be stress-related. Persistent or severe diarrhea after boarding should be discussed with a veterinarian.
What does it mean if my dog's diarrhea has mucus in it?
Small amounts of mucus are sometimes present with mild intestinal irritation and may resolve on their own. However, larger amounts of mucus, especially when combined with blood or frequent episodes, may indicate inflammation or infection and should be evaluated by a veterinarian.
SYMPTOM TRIAGE
If your dog has diarrhea and you are unsure how serious it may be, use the symptom triage tool to receive general guidance on whether and how quickly to seek veterinary care.
Sources
- American Kennel Club. "Diarrhea in Dogs: Causes, Treatment, and When to Worry." Retrieved July 2026.
- Cornell University College of Veterinary Medicine. "Gastrointestinal Parasites of Dogs." Retrieved July 2026.
- Merck Veterinary Manual. "Diarrhea in Small Animals." Retrieved July 2026.
- U.S. Food and Drug Administration (FDA). "Pet Food Safety." Retrieved July 2026.
This article and the PawAI Symptom Triage tool provide general educational information only. They cannot examine your pet, make a diagnosis, or replace advice from a licensed veterinarian. Contact a veterinarian promptly if symptoms are severe, worsening, persistent, or accompanied by emergency warning signs.