Diarrhea in cats is most often triggered by something the cat ate, but it can also signal infections, parasites, chronic digestive diseases, or medication side effects. A single episode of loose stool usually resolves on its own, while diarrhea lasting more than a day or two, or accompanied by vomiting, blood, or lethargy, points to something that needs veterinary attention.
Dietary Changes and Food Reactions
The simplest and most common cause is dietary. Cats have sensitive digestive systems, and even a well-intentioned switch to a new food can set off a bout of loose stool if the transition happens too quickly. Table scraps, garbage raiding, or getting into something they shouldn’t have (what vets call “dietary indiscretion”) are frequent culprits, especially in cats with outdoor access or curious temperaments.
Food intolerances and allergies can also cause recurring diarrhea. Some cats react to specific proteins in their diet. If your cat’s diarrhea keeps coming back despite no obvious dietary mishaps, the food itself may be the problem. Keeping your cat on a consistent diet of quality cat food, without table scraps or frequent brand switches, is one of the easiest ways to prevent digestive upset.
Bacterial and Viral Infections
Several infectious agents target a cat’s gut. On the bacterial side, Campylobacter and Clostridium are among the most commonly identified in cats with diarrhea. Cats can pick these up from contaminated food, water, or contact with infected animals. Clostridium difficile, in particular, has been linked to cats that have recently been on antibiotics or other medications that disrupt normal gut bacteria.
The most serious viral cause is feline panleukopenia, caused by a parvovirus. It’s highly contagious, hits kittens hardest, and causes severe, often bloody diarrhea along with vomiting, fever, and a dangerous drop in white blood cells. Vaccination is extremely effective at preventing it, which is why it’s part of the core vaccine schedule for kittens.
Intestinal Parasites
Parasites are a leading cause of diarrhea in kittens and outdoor cats, though indoor cats aren’t immune.
Giardia is a microscopic parasite that causes acute or chronic diarrhea, though most infected cats actually show no symptoms at all. Diagnosing it can be tricky because the organism isn’t shed continuously in the stool. Your vet may need to test multiple fecal samples to catch it.
Coccidia (specifically Isospora species) rarely causes problems in adult cats, but in kittens it can destroy the intestinal lining, leading to mucousy diarrhea, vomiting, and poor appetite. It’s diagnosed by finding microscopic cysts in a stool sample.
Roundworms (Toxocara) are another common parasite, particularly in kittens who can acquire them from their mother’s milk. Cryptosporidium and Tritrichomonas round out the list of parasites frequently identified in cats with persistent loose stool. Regular deworming and fecal testing, especially for kittens and cats that go outdoors, helps catch these early.
How Diarrhea Actually Works in the Gut
Not all diarrhea is the same mechanically. Understanding the type can help explain why your cat’s symptoms look the way they do.
Osmotic diarrhea happens when unabsorbed food or other substances in the intestine pull water into the gut. This is common when the intestinal lining is damaged, since the cells responsible for absorbing nutrients and water aren’t working properly. The food stays in the gut, creates a concentration imbalance, and water follows. This is often what’s happening with parasitic infections or food intolerances.
Secretory diarrhea is the opposite direction: the gut actively pumps too much fluid into the intestinal space, overwhelming the body’s ability to reabsorb it. Certain bacterial toxins can trigger this type.
Inflammatory diarrhea involves direct leakage of fluid and proteins through a damaged, inflamed intestinal wall. This is the mechanism behind conditions like inflammatory bowel disease. Faster-than-normal gut motility, where food moves through too quickly for water to be absorbed, can layer on top of any of these types and make things worse.
Chronic Conditions: IBD and Lymphoma
When diarrhea persists for weeks or keeps recurring despite treatment, chronic disease becomes a concern. Inflammatory bowel disease is one of the most common chronic causes in cats, particularly in middle-aged and older animals. IBD involves persistent inflammation of the intestinal wall, leading to poor nutrient absorption and ongoing digestive symptoms. The cause isn’t fully understood, but it likely involves an abnormal immune response to something in the gut environment.
Complicating matters, intestinal lymphoma (a type of cancer) can look nearly identical to IBD on initial testing. Distinguishing between the two often requires a biopsy. Hyperthyroidism, which is common in older cats, can also cause chronic diarrhea and is something vets screen for during workup. If your older cat has persistent loose stools and is losing weight, these are the conditions your vet will be evaluating.
Medications and Toxins
Antibiotics are a frequent medication-related cause. They can wipe out beneficial gut bacteria along with harmful ones, creating an imbalance that leads to diarrhea. Ironically, antibiotics are sometimes prescribed to treat diarrhea, but using them for uncomplicated or non-infectious cases can actually make things worse by further disrupting the intestinal microbiome and promoting resistant bacteria.
Chemotherapy drugs and certain other medications also list diarrhea as a side effect. If your cat develops loose stool shortly after starting any new medication, that connection is worth flagging with your vet. Household toxins, certain plants, and chemical exposures can trigger diarrhea too, though cats tend to be more cautious eaters than dogs.
Probiotics for Recovery
There’s reasonable evidence that probiotics can help cats recover from diarrhea faster. In shelter cats, those given a specific probiotic strain (Enterococcus faecium SF68) were less likely to have diarrhea lasting more than two days compared to cats given a placebo. The results were even more striking in kittens during a diarrhea outbreak: kittens given the probiotic resolved their symptoms in about 18 days versus 45 days for those that didn’t receive it, and only 9.5% needed additional medical treatment compared to 60% of the control group.
Cats with chronic, undefined diarrhea also showed fewer episodes of severe diarrhea when given this probiotic. Probiotics aren’t a replacement for diagnosing and treating the underlying cause, but they can be a useful add-on, especially during recovery.
Signs That Need Prompt Attention
A single day of soft stool in an otherwise bright, active cat is usually not an emergency. What changes the picture is severity and accompanying symptoms. Bloody diarrhea, weakness, fever, vomiting, abdominal pain, loss of appetite, or visible dehydration all signal that something more serious is going on.
You can check for dehydration at home by gently lifting the skin over your cat’s shoulders and releasing it. In a well-hydrated cat, the skin snaps back immediately. If it stays “tented” or returns slowly, your cat is likely dehydrated. Other signs include dry, tacky gums, sunken eyes, and overall lethargy. One caveat: older cats often have reduced skin elasticity even when they’re perfectly hydrated, so skin tenting alone isn’t as reliable in senior cats. Persistent diarrhea in kittens is always worth taking seriously, since their smaller size makes them vulnerable to dehydration much faster than adult cats.