Chronic Diarrhea in Dogs: Causes and Veterinary Considerations
One bout of loose stool is rarely a crisis. But when diarrhea keeps coming back — or never fully resolves — something deeper may be going on.
What you need to know
Diarrhea in dogs is one of the most common reasons for veterinary visits. An occasional soft stool can be completely normal. But when diarrhea recurs frequently, lasts more than a few days, or keeps cycling back despite home management, it's considered chronic — and it warrants a thorough veterinary evaluation.
Chronic diarrhea in dogs is not a diagnosis. It's a symptom. The underlying cause can range from a simple dietary issue to a complex inflammatory disease — and identifying the right cause is essential to finding the right treatment.
Veterinary guidelines generally define chronic diarrhea as diarrhea lasting more than 3 weeks, or acute diarrhea that recurs frequently. Some clinicians use a 2-week threshold. Duration alone doesn't define severity — a dog can have chronic soft stool with otherwise normal energy and appetite, or can be significantly unwell with weight loss and lethargy.
Small intestine vs large intestine diarrhea
One of the first things your veterinarian will try to determine is where in the GI tract the problem is originating. The two types look and behave differently:
Small intestinal diarrhea tends to involve:
- Large volumes of watery or soft stool
- Possible weight loss or poor body condition
- Reduced frequency (normal or slightly increased number of bowel movements)
- Possible dark or tarry stool if there's bleeding higher in the GI tract
- Vomiting may accompany GI upset
Large intestinal (colonic) diarrhea tends to involve:
- More frequent, smaller-volume bowel movements
- Straining or urgency to defecate
- Presence of fresh red blood or mucus in the stool
- Weight is often maintained
Some dogs have mixed patterns affecting both sections of the bowel. This distinction helps guide testing and treatment decisions.
Common causes of chronic diarrhea in dogs
There are many possible causes, which is why veterinary investigation is important. The most common categories include:
Dietary causes
- Food sensitivity or adverse food reaction — A response to a specific protein or ingredient in the diet (discussed further in Guide 06)
- Dietary indiscretion — Repeated access to trash, table scraps, or novel foods
- Abrupt diet changes — Switching foods too quickly without a gradual transition
- High-fat diets — May trigger chronic soft stool in some dogs
Infectious causes
- Parasites — Giardia, Tritrichomonas, hookworms, whipworms, roundworms
- Bacterial overgrowth — Small intestinal dysbiosis
- Clostridioides difficile and other bacterial pathogens
Inflammatory and immune-mediated causes
- Inflammatory bowel disease (IBD) — A chronic immune-mediated condition affecting the GI tract lining
- Protein-losing enteropathy (PLE) — Severe inflammatory disease causing protein loss through the gut
- Lymphoma — GI lymphoma can mimic IBD and may require biopsy to distinguish
Organ-related causes
- Exocrine pancreatic insufficiency (EPI) — The pancreas doesn't produce enough digestive enzymes; often causes large-volume, greasy stool and weight loss
- Liver disease — Can affect bile production and stool consistency
- Hypoadrenocorticism (Addison's disease) — A hormonal condition that can cause GI symptoms including chronic diarrhea
Other causes
- Stress and anxiety (discussed in Guide 07)
- Medication side effects
- Structural issues (polyps, foreign bodies in rare chronic cases)
Treating chronic diarrhea without knowing the cause is often ineffective and sometimes counterproductive. For example, a bland diet may help a food-sensitive dog but will do little for a dog with EPI, which requires enzyme supplementation. And IBD, if severe, typically requires immunosuppressive medication that wouldn't be appropriate for a dog with a parasitic infection. Diagnostic workup guides appropriate treatment.
What veterinary investigation typically involves
Depending on your dog's history, duration of symptoms, and physical exam findings, your vet may recommend:
- Fecal testing — Fecal flotation for parasites, fecal PCR panel for Giardia, Tritrichomonas, and other pathogens
- Blood work — Complete blood count, chemistry panel, cobalamin (B12) and folate levels, TLI (trypsin-like immunoreactivity) for EPI
- Urinalysis — Rules out other systemic disease
- Dietary trial — A structured hydrolyzed or novel-protein elimination diet to test for food-responsive disease (typically 6–8 weeks minimum)
- Abdominal ultrasound — Assesses gut wall thickness, lymph nodes, and other organs
- Endoscopy and biopsy — Definitive diagnosis for IBD, lymphoma, and other mucosal disease
- Bring a fresh stool sample (within 4–6 hours) in a clean, sealed container
- Note the stool consistency using the Fecal Scoring Scale (1–7, where 2 is ideal and 5–7 is diarrhea)
- Record when symptoms started, how frequently they occur, and any patterns (morning vs evening, after eating, after stress)
- List all foods, treats, chews, and supplements your dog currently receives
- Note any recent antibiotic use, travel, or exposure to other animals
- Track whether your dog's weight has changed
When to contact your veterinarian urgently
- Bloody diarrhea — especially large amounts of fresh or dark blood
- Diarrhea combined with vomiting and lethargy
- Obvious weight loss or muscle wasting
- Signs of dehydration (dry or tacky gums, reduced skin elasticity, sunken eyes)
- Abdominal pain or distension
- Any diarrhea in puppies, geriatric dogs, or dogs with known health conditions — these groups dehydrate faster and may deteriorate quickly
- Diarrhea not improving or worsening after 72 hours
Common myths
Myth: "A bland diet always fixes diarrhea"
Bland diets (such as boiled chicken and rice) can be helpful for mild, acute GI upset. For chronic diarrhea, they may provide temporary relief without addressing the underlying cause. Some dogs on elimination dietary trials should not receive chicken and rice, as chicken is a common allergen. Always confirm dietary recommendations with your vet for chronic or recurring symptoms.
Myth: "If my dog has normal energy, the diarrhea isn't serious"
Dogs can appear fairly normal in the early stages of conditions like IBD, EPI, or protein-losing enteropathy. Weight loss and subtle changes in coat quality may precede obvious systemic illness. Don't use energy level alone as a gauge of GI health — duration and pattern of diarrhea matter.
Myth: "Fasting for 24 hours is always the right first step"
Fasting used to be routinely recommended for GI upset. Current veterinary thinking is more nuanced — brief food restriction may be appropriate in some adult dogs with acute diarrhea, but it is generally not recommended for puppies, small breeds, diabetic dogs, or dogs with underlying disease who need caloric intake. Ask your vet before withholding food.
- Chronic diarrhea is defined as diarrhea lasting 3+ weeks or recurring frequently — it's a symptom, not a diagnosis
- There are many possible causes including dietary, infectious, inflammatory, and organ-related conditions
- Knowing whether diarrhea originates in the small or large intestine helps guide diagnosis
- Veterinary workup — including fecal testing, blood work, and sometimes imaging or biopsy — is often needed to find the cause
- Treating without a diagnosis may delay effective care
- Bring stool samples, a symptom log, and a complete diet history to your vet appointment
- Seek urgent care for bloody diarrhea, significant lethargy, weight loss, or any diarrhea in puppies or senior dogs
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- Suchodolski JS, Jergens AE. Recent advances and understanding of using probiotic-based interventions to restore homeostasis of the canine and feline gut microbiome. Veterinary Clinics of North America: Small Animal Practice. 2022;52(3):683–696. doi.org/10.1016/j.cvsm.2022.01.007
- Westermarck E, Wiberg M. Exocrine pancreatic insufficiency in dogs. Veterinary Clinics of North America: Small Animal Practice. 2003;33(5):1165–1179. doi.org/10.1016/S0195-5616(03)00057-6
- Rudinsky AJ, Rowe JC, Parker VJ. Nutritional management of chronic enteropathies in dogs and cats. Journal of the American Veterinary Medical Association. 2018;253(5):570–578. doi.org/10.2460/javma.253.5.570
- Purina Institute. Fecal scoring guide. purinainstitute.com
Last reviewed by PetGutHealth: June 2026
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Content on PetGutHealth is for educational purposes only and is not veterinary medical advice. Always consult your veterinarian regarding your pet's health.