SYMPTOM
Chronic diarrhoea
Persistent loose or watery stools lasting weeks or longer, sometimes alternating with periods of normal consistency.
Inflammatory bowel disease
Chronic inflammation of the intestinal wall — involving various types of inflammatory cell infiltration — is one of the more common causes of persistent diarrhoea in dogs and cats. The inflammation disrupts normal intestinal absorption and motility, producing loose stools that may be accompanied by weight loss, altered appetite, and sometimes vomiting. The condition can affect any part of the gastrointestinal tract and tends to follow a relapsing-remitting course.
Dietary sensitivity or intolerance
Adverse reactions to specific dietary components — whether true food allergies involving immune responses or non-immunological intolerances — can produce chronic diarrhoea that persists as long as the triggering food is consumed. Common triggers may include specific proteins, carbohydrates, or additives. The diarrhoea may fluctuate with dietary changes and can be accompanied by other signs such as skin irritation, flatulence, or vomiting.
Exocrine pancreatic insufficiency
When the pancreas produces insufficient digestive enzymes, food passes through the gastrointestinal tract without being properly broken down and absorbed. This produces characteristic large-volume, pale, fatty stools that may have an unusually strong odour. Animals with this condition often lose weight despite eating large quantities of food and may develop a ravenous appetite as their body struggles to obtain adequate nutrition from incompletely digested meals.
Intestinal parasites
While often associated with acute diarrhoea, certain intestinal parasites can produce chronic or recurring loose stools, particularly in young animals, immunocompromised individuals, or those with heavy parasite burdens. Giardia, whipworms, and certain coccidia species are among the organisms that may cause persistent diarrhoea. The pattern may wax and wane with the parasite's lifecycle, and standard faecal testing may not always detect all organisms on a single sample.
Dysbiosis
Disruption of the normal intestinal microbiome — the community of bacteria, fungi, and other organisms inhabiting the gut — can contribute to chronic diarrhoea. Dysbiosis may develop following antibiotic use, dietary changes, stress, or as a consequence of other gastrointestinal conditions. The altered microbial population can affect intestinal function, barrier integrity, and the fermentation processes that normally contribute to stool formation.
Neoplastic
Tumours affecting the intestinal wall, mesenteric lymph nodes, or associated structures can cause chronic diarrhoea, particularly in older animals. Intestinal lymphoma, adenocarcinoma, and other intestinal tumours may produce progressive diarrhoea alongside weight loss and declining appetite. The diarrhoea pattern depends on the location and extent of the tumour, with masses in the small intestine often producing different stool characteristics than those in the large intestine.
Why timing matters
Early observation
When chronic diarrhoea is first recognised as a persistent pattern rather than an isolated episode, it may reflect an ongoing inflammatory, infectious, or dietary process within the gastrointestinal tract. Early chronic diarrhoea often presents as soft or loose stools that occur more frequently than normal, sometimes alternating with periods of near-normal consistency. Owners may initially attribute the changes to dietary indiscretion, stress, or environmental factors. The transition from acute to chronic diarrhoea — generally considered to be persistence beyond two to three weeks — suggests that the cause has not self-resolved and an ongoing process is at work.
Later presentation
Chronic diarrhoea that continues for months or progressively worsens may indicate a well-established gastrointestinal condition that is unlikely to resolve without identification and management of the underlying cause. As the condition persists, secondary effects may become apparent: weight loss despite adequate food intake, changes in coat quality, reduced energy levels, or the development of nutrient deficiencies. The character of the diarrhoea may also evolve, with changes in colour, consistency, presence of mucus or blood, or volume providing clues about whether the small intestine, large intestine, or both are involved.
The trajectory of chronic diarrhoea varies considerably. Some animals develop a stable pattern of intermittently loose stools that persists without significant worsening, while others experience a progressive deterioration in stool quality over time. Dietary-responsive conditions may fluctuate with food changes, producing periods of improvement followed by relapse. Inflammatory bowel conditions may follow a waxing and waning course, with periods of relative normalcy interspersed with flare-ups. Progressive weight loss, increasing frequency, or the appearance of blood or mucus in stools may indicate that the underlying condition is advancing or that complications are developing.
Conditions commonly associated
Inflammatory Bowel Disease in Dogs
Inflammatory Bowel Disease in Cats
Food Allergy in Dogs
Food allergy can produce chronic gastrointestinal signs including persistent soft stools, increased stool frequency, and diarrhoea. The inflammatory response to dietary proteins affects the intestinal mucosa, and GI signs may occur alongside or independently of skin manifestations.
Gastroenteritis in Dogs
Diarrhoea is a defining feature of gastroenteritis, and chronic or recurrent episodes may suggest ongoing inflammatory processes in the gastrointestinal tract.
Lymphoma in Cats
Chronic diarrhoea frequently accompanies alimentary lymphoma in cats as lymphocytic infiltration of the intestinal wall impairs nutrient absorption, disrupts the mucosal barrier, and alters intestinal motility patterns.
Exocrine Pancreatic Insufficiency (EPI)
Chronic diarrhoea with characteristically large, pale, greasy stools is a hallmark of EPI, reflecting the maldigestion of fats and other nutrients.
Feline Immunodeficiency Virus (FIV)
Chronic diarrhoea in FIV-positive cats may result from opportunistic gastrointestinal infections, immune-mediated inflammatory bowel changes, or disruption of normal gut flora as immune surveillance diminishes.
Triaditis in Cats
Intestinal inflammation in triaditis can result in chronic diarrhoea as nutrient absorption is impaired.
Gastroenteritis in Cats
Persistent loose stools may accompany or follow acute gastroenteritis episodes in cats.
Colitis
Colitis commonly causes frequent loose stools as the inflamed colon cannot properly absorb water or form normal faeces.
Intestinal Parasites
Intestinal parasites can irritate the gut lining and disrupt normal digestion, often resulting in loose or poorly formed stools.
Giardiasis
Persistent or intermittent diarrhoea with characteristically pale, greasy, and malodorous stools is a hallmark of giardiasis.
When to explore further
Diarrhoea that has persisted for more than two to three weeks without resolution, particularly if dietary adjustments and routine parasite management have not improved the situation, suggests a process that may benefit from further investigation.
When chronic diarrhoea is accompanied by progressive weight loss, despite the animal eating normally or even more than usual, this combination may indicate a malabsorptive or maldigestive process that warrants closer assessment.
The presence of blood in the stool — whether fresh red blood (suggesting large intestinal involvement) or dark, tarry stools (suggesting upper gastrointestinal bleeding) — alongside chronic diarrhoea adds important clinical context.
Chronic diarrhoea accompanied by vomiting, reduced appetite, or lethargy suggests that the gastrointestinal condition may be affecting the animal's overall wellbeing beyond just stool changes.
A significant change in the character of chronic diarrhoea — from intermittent to constant, from mild to severe, or with the new appearance of blood or mucus — may indicate progression or complication of the underlying process.
Observing and noting the characteristics of the diarrhoea — frequency, volume, colour, consistency, presence of mucus or blood, and whether urgency or straining is present — can help distinguish between small intestinal and large intestinal patterns. Tracking whether the diarrhoea correlates with specific dietary components, stress events, or other environmental factors may also help identify contributing triggers over time.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS