# Why Does My Cat Keep Getting Diarrhea? Causes and Next Steps If your cat's diarrhea keeps coming back, the cause is often something that was never fully identified or fully treated the first time. Short bouts usually trace to diet changes or stress, but diarrhea that returns again and again points to a longer list of possibilities, including parasites, food intolerance, chronic enteropathy, and viral or bacterial infections [1][2]. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## Quick Answer - Diarrhea lasting three weeks or longer is called chronic diarrhea, and it needs a real diagnostic plan, not just repeated diet swaps [3]. - A single bout after a food change or a stressful trip is common and often settles on its own within a few days [1]. - Recurring diarrhea in cats is often linked to diet, parasites, or chronic enteropathy, and the treatment for each is different [2]. - Feline coronavirus was found in 65.1% of cats with chronic diarrhea in one large study, so a positive test alone does not prove it is the cause [4]. - If your cat is vomiting, losing weight, or acting sick, that moves the visit from routine to urgent. ## What Normal and Abnormal Stool Looks Like Normal cat stool is formed, log shaped, and easy to pick up. It holds its shape without leaving much residue on the litter or the scoop. Diarrhea is the frequent passage of watery stool, and it may look gray or yellow and smell unusually foul [1]. Some cats have accidents outside the box because they cannot get there in time. Others strain and produce only small amounts. Vets split diarrhea into two rough groups based on where it starts. Small bowel diarrhea tends to produce large volumes of stool, often with weight loss. Large bowel diarrhea tends to come with mucus, urgency, and more frequent small trips to the box [2]. That distinction shapes which tests your vet runs first. If you are seeing mucus specifically, [Cat Diarrhea with Mucus: Causes and When to Worry](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-with-mucus-causes-when-to-worry) walks through what that usually means. ## Why Cat Diarrhea Keeps Coming Back: The Main Causes Recurring diarrhea in cats rarely has one simple trigger. It usually comes down to a cause that was missed, a cause that was treated but not resolved, or a condition that flares in cycles. ### Diet and food intolerance An abrupt diet change can cause diarrhea for a few days, and that is normal [1]. The problem is when owners switch foods repeatedly to chase the symptom. Each switch can restart the irritation, so the diarrhea never fully clears. Food intolerance and food-responsive enteropathy are common in cats with long-running diarrhea. These cats often improve on a specific therapeutic diet, but only if the diet is fed exclusively for long enough to judge the response [2][5]. ### Parasites and infectious causes Giardia and other intestinal parasites are a well-known cause of intermittent diarrhea. In one study of cats with chronic diarrhea, Giardia was found in 8.4% of fecal samples [4]. That is a meaningful number, and it is one reason fecal testing matters even in cats that seem otherwise healthy. Clostridium perfringens toxin DNA showed up in 54.4% of samples in that same study, and 35.2% of samples carried both feline coronavirus and C. perfringens [4]. These findings do not automatically mean the organism is the culprit, but they do change what your vet looks for. ### Chronic enteropathy and inflammatory bowel disease Feline chronic enteropathy is the umbrella term for gastrointestinal signs lasting at least three weeks. The most common final diagnoses are inflammatory bowel disease and alimentary small cell lymphoma [3]. These conditions often cause waxing and waning diarrhea, which is exactly why owners describe it as "it keeps coming back." The microbiome is thought to play a role in these diseases, including changes in the composition and function of intestinal bacteria and in the fatty acids they produce [3]. That is one reason diet and gut support are part of long-term management. ### Viral and bacterial contributors Feline coronavirus was detected in 65.1% of cats with chronic diarrhea in a large specialty practice review [4]. It was the only pathogen found in 23.9% of those cats [4]. Cats under one year old were significantly more likely to test positive than older cats [4]. That does not mean coronavirus is always the cause. It means the picture is complicated, and a single positive test does not close the case. ### Stress and environment Stress can trigger a short episode of loose stool. A long car trip or a weekend at a veterinary clinic is enough to do it [1]. In a cat with an underlying gut condition, stress can also be the thing that tips a stable cat back into a flare. ### Medication side effects Some medications cause diarrhea as a side effect. If the timing lines up with a new drug or a dose change, that is worth raising with your vet. [What to Do If Your Cat's Medication Is Causing Diarrhea](/knowledge/veterinary-medicine/pet-medication-guide/cat-medication-diarrhea-what-to-do) covers how to handle that conversation safely. ## Cause, Clues, and Urgency at a Glance | Cause | Typical clues | How urgent | |---|---|---| | Diet change or food intolerance | Loose stool starting within days of a new food, otherwise bright cat | Routine visit if it lasts more than a couple of days | | Parasites (such as Giardia) | Intermittent soft stool, sometimes mucus, possible weight loss | Routine visit, bring a fresh fecal sample | | Chronic enteropathy or IBD | Diarrhea lasting three weeks or more, weight loss, waxing and waning | Routine but prompt visit, needs diagnostics [3] | | Feline coronavirus or other viral infection | Chronic diarrhea, more common in cats under one year [4] | Routine visit, testing guides next steps | | Bacterial overgrowth or toxin producers | Sudden worsening, sometimes with vomiting | Same-day call if the cat seems unwell | | Stress | Loose stool around travel, boarding, or household change | Monitor, call if it persists [1] | | Medication side effect | Diarrhea starting after a new drug | Call the prescribing vet before stopping anything | ## Red Flags That Mean Emergency Care Now Some signs mean you should not wait for a routine appointment. - Repeated vomiting with diarrhea, especially if your cat cannot keep water down. - Blood in the stool, or black tarry stool. - A cat that is weak, wobbly, or hard to wake. - A cat that has stopped eating for more than a day. - Signs of pain, such as crying out, hiding, or a tense belly. - A kitten with diarrhea, since young cats dehydrate fast. - Any cat that looks dehydrated, with tacky gums or skin that stays tented. If any of these appear, call an emergency clinic right away. Do not try home remedies first. ## Safe Things You Can Do at Home While You Wait You cannot diagnose your cat at home, but you can avoid making things worse. ### Stop switching foods Pick one food and stay with it until your vet weighs in. Every new bag or can restarts the clock and makes a diet trial impossible to interpret [2]. ### Keep a simple log Write down the date, stool consistency, how many times a day, and anything new in the environment or diet. Patterns show up fast in a written log, and your vet can use it. ### Keep fresh water available Cats with diarrhea lose fluid. Offer clean water in several spots and consider a water fountain if your cat prefers running water. ### Do not give human medications Never give over-the-counter diarrhea medicine to a cat unless your veterinarian specifically prescribes it. Doses depend on your cat's weight and health, and your vet calculates them for your pet. ### Collect a stool sample A fresh sample, ideally less than a few hours old, can save a return trip. Your vet can tell you how to store it. ### Keep the litter box clean Scoop more often than usual so you can see exactly what is coming out and how often. If the diarrhea started right after a meal, [Cat Diarrhea After Eating: Causes and When to Act](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-after-eating) explains the timing patterns that matter. ## What Your Veterinarian Will Check and Test Expect a full physical exam first. Your vet will check hydration, weight, body condition, and feel your cat's abdomen. Weight trend matters a lot in chronic cases. ### Fecal testing Fecal flotation and other stool tests look for parasites such as Giardia [4]. A PCR panel can check for several organisms at once, including coronavirus and Clostridium perfringens toxin DNA [4]. Because these organisms can be present without causing disease, results are read alongside the exam and history. ### Blood work A complete blood count and chemistry panel check for anemia, organ problems, and protein loss. Low protein or low cobalamin can point toward a chronic enteropathy. ### Imaging X-rays or ultrasound help your vet look at the intestinal wall, lymph nodes, and other organs. Ultrasound is often more useful for chronic cases. ### Diet trial A proper diet trial means feeding one therapeutic diet exclusively for a set period, with no treats, table food, or other pets' food. Your vet sets the length based on your cat's case. Improvement during a trial is itself a diagnostic result [2][5]. ### Biopsy in some cases If the workup points to inflammatory bowel disease or lymphoma, your vet may recommend intestinal biopsy. This is the only way to tell those two apart with confidence. ### Treatment planning Treatment depends on what is found. It may include antiparasitics, a therapeutic diet, cobalamin supplementation, or immune-suppressing medication. In one published case, a cat with chronic nonresponsive enteropathy and diabetes improved after being transitioned to a high-protein, low-carbohydrate commercial veterinary therapeutic diet, with clinical signs improving over five days and insulin discontinued at discharge after six days of hospitalization [5]. Psyllium husk was later added to improve stool quality, and soft stools persisted for several months before normalizing [5]. That timeline is a useful reality check. Chronic gut cases often improve slowly. ## Preventing and Monitoring Recurring Diarrhea You cannot prevent every cause, but you can reduce the odds of a repeat. - Change foods gradually when you must change, and give any new diet a real trial before judging it [2]. - Keep up with parasite prevention as your vet recommends. - Bring a fecal sample to routine visits if your cat has had diarrhea before. - Track weight at home if you can, since weight loss is a common clue in chronic enteropathy [3]. - Watch for seasonal patterns. In one study, coronavirus detection peaked in February and March [4]. - Keep stress low around travel and household changes, since stress alone can trigger loose stool [1]. If your cat has had more than two separate episodes in a few months, ask your vet whether a full chronic diarrhea workup makes sense. Repeated short courses of treatment without a diagnosis is how diarrhea keeps coming back. ## Limitations and When to Contact a Veterinarian This article cannot tell you what is causing your cat's diarrhea. Only your veterinarian can do that after an exam and testing. Individual cases need individual care. Call the same day if your cat has diarrhea plus vomiting, is eating less, is losing weight, or has had loose stool for more than two days. Go to an emergency clinic now if you see blood, black stool, repeated vomiting, weakness, collapse, or a kitten with diarrhea. Dehydration can become dangerous quickly in young cats. Schedule a routine visit if the diarrhea keeps returning but your cat is otherwise bright, eating, and drinking. Bring a fresh stool sample and your log. For a broader look at home care and when to escalate, see [Cat Diarrhea: Causes, Home Care, and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-diarrhea-causes-home-care) and [Cat Diarrhea: When Should You Call the Vet?](/knowledge/veterinary-medicine/symptom-guides/cat-diarrhea-when-to-call-vet). ## Frequently Asked Questions ### How long is too long for cat diarrhea? Three weeks or more is the standard cutoff for chronic diarrhea, and it should trigger a full workup [3]. Anything shorter can still need a visit if your cat is vomiting, losing weight, or acting sick. A single mild episode after a food change often settles within a few days [1]. ### Can stress alone cause recurring diarrhea in my cat? Stress can cause a brief episode of loose stool, such as after a long car trip or a clinic stay [1]. Stress is less likely to be the only cause of diarrhea that returns for weeks or months. In cats with an underlying gut condition, stress often acts as a trigger for flares. ### Does a positive coronavirus test mean my cat has a chronic illness? No. Feline coronavirus was found in a majority of cats with chronic diarrhea in one large study, but it is also common in the general cat population [4]. A positive result is one piece of information, not a diagnosis. Your vet will interpret it with the exam, history, and other tests. ### Will a grain-free or limited-ingredient diet fix my cat's diarrhea? Not automatically. What matters is whether the diet is a true therapeutic trial, fed exclusively for the right length of time [2]. Many over-the-counter limited-ingredient diets are not strict enough for a diagnostic trial. Ask your vet which diet fits your cat's case. ### Can my cat's medication be causing the diarrhea to come back? It is possible. Some drugs cause diarrhea as a side effect, and the timing with a new medication or dose change is a clue. Do not stop a prescribed medication on your own. Call the prescribing veterinarian and describe what you are seeing. ## Related Articles - [Cat Diarrhea: Causes, Home Care, and When to Worry](/knowledge/veterinary-medicine/online-vet-and-care-costs/cat-diarrhea-causes-home-care) - [What to Do If Your Cat's Medication Is Causing Diarrhea](/knowledge/veterinary-medicine/pet-medication-guide/cat-medication-diarrhea-what-to-do) - [Cat Diarrhea After Eating: Causes and When to Act](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-after-eating) - [Cat Diarrhea with Mucus: Causes and When to Worry](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-diarrhea-with-mucus-causes-when-to-worry) - [Cat Diarrhea: When Should You Call the Vet?](/knowledge/veterinary-medicine/symptom-guides/cat-diarrhea-when-to-call-vet) - [Kitten Diarrhea: Causes, Safe Home Care, and Emergency Signs](/knowledge/veterinary-medicine/digestive-and-urinary-care/kitten-diarrhea-causes-and-care) - [Why Is My Cat Suddenly Having Diarrhea? Causes and Care](/knowledge/veterinary-medicine/digestive-and-urinary-care/why-is-my-cat-suddenly-having-diarrhea) - [Long-Term Diarrhea in Cats: Causes and Next Steps](/knowledge/veterinary-medicine/digestive-and-urinary-care/long-term-diarrhea-in-cats) - [Cat Diarrhea On and Off: Causes of Intermittent Loose Stool](/knowledge/veterinary-medicine/digestive-and-urinary-care/cat-intermittent-diarrhea) ## References 1. [Diarrhea](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/diarrhea). Cornell University College of Veterinary Medicine. 2. [Feline chronic diarrhea: causes and nutritional management](https://pubmed.ncbi.nlm.nih.gov/42502773/). Veterinary and animal science, 2026. 3. [Faecal microbiota and fatty acids in feline chronic enteropathy](https://pubmed.ncbi.nlm.nih.gov/38124157/). BMC veterinary research, 2023. 4. [Feline Coronavirus Prevalence in 493 Cats With Chronic Diarrhea](https://pubmed.ncbi.nlm.nih.gov/41771138/). Journal of veterinary internal medicine, 2025. 5. [Nutritional management of feline chronic enteropathy with evolving dietary response and long-term stabilization](https://pubmed.ncbi.nlm.nih.gov/42544297/). The Canadian veterinary journal = La revue veterinaire canadienne, 2026. ## Further Reading - [Merck Veterinary Manual: Cat Owners](https://www.merckvetmanual.com/cat-owners) - [Cornell Feline Health Center: Health Information](https://www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information) - [American Veterinary Medical Association: Pet Care](https://www.avma.org/resources-tools/pet-owners/petcare)