Diarrhea in cats is usually caused by irritation or disease in the digestive tract, and it can range from mild and temporary to a sign of something serious that needs a vet visit.

Main causes of diarrhea in cats (Quick Scoop)

Think of a cat’s gut like a very sensitive conveyor belt: anything that upsets the lining, the bacteria, or how it moves can lead to loose stool.

1. Food and diet issues

  • Sudden change in food (switching brands or flavors too fast can upset the gut).
  • Eating garbage or spoiled food, including food from the trash or old wet food left out too long.
  • Food intolerance or sensitivity (for example to certain proteins, additives, or ingredients). Vets often suspect this with recurring loose stools.
  • Dairy such as cow’s milk, because most cats are lactose intolerant and can’t digest lactose properly.

2. Infections (viral, bacterial, parasitic)

  • Intestinal parasites (roundworms, tapeworms, giardia) are especially common in kittens and can cause severe diarrhea and weight loss.
  • Viral infections such as feline panleukopenia, feline leukemia virus, or other GI viruses can trigger vomiting and watery stool, especially in unvaccinated or young cats.
  • Bacterial infections (for example Salmonella or E. coli) from contaminated food, raw meat, or spoiled food can inflame the intestines and cause diarrhea.

3. Stress and environmental changes

  • Stress or anxiety from moving house, new pets, boarding, loud remodeling, or even a new baby can speed up gut movement and cause loose stool.
  • Some cats have very “nervous” guts that flare during any change in routine, similar to stress-triggered stomach issues in people.

4. Inflammatory and chronic gut disease

  • Colitis (inflammation of the colon) often causes frequent, small amounts of soft or liquid stool, sometimes with mucus or blood.
  • Inflammatory bowel disease (IBD) and other primary inflammatory disorders disturb the intestinal lining, leading to chronic or recurring diarrhea, weight loss, or vomiting.
  • These conditions may need long‑term management (special diets, medications) guided by a veterinarian.

5. Toxins, medications, and foreign objects

  • Toxins or poisons , including certain plants, household cleaners, and human medications, can irritate the gut and cause diarrhea along with other signs like drooling, lethargy, or vomiting.
  • Some medications (notably antibiotics and some other drugs) can disrupt normal gut bacteria or irritate the GI tract and cause loose stool.
  • Swallowing foreign objects (string, fabric, toys, plastic) can partially block the intestines, leading to diarrhea, pain, and sometimes vomiting; this can become an emergency.

6. Organ disease and metabolic problems

  • Liver disease or kidney disease can change how the body handles toxins and fluids, upsetting the gut and causing diarrhea.
  • Pancreatitis (inflammation of the pancreas) and other metabolic diseases can disturb digestion and cause chronic or intermittent diarrhea, often with poor appetite and lethargy.
  • Thyroid and pancreatic imbalances can alter gut motility and lead to loose stool as part of a broader illness picture.

7. Kittens vs adult cats

  • Kittens are more likely to have diarrhea from parasites, diet changes, viruses, and eating inappropriate objects.
  • Older cats may show diarrhea linked to constipation with overflow (small amounts of liquid stool leaking around a blockage), organ disease, or tumors.

Mini story: Imagine a young indoor cat who suddenly has loose stool right after their owner switches to a rich, high‑fat wet food and offers a saucer of milk “as a treat.” Within a day, there’s smelly diarrhea in the litter box. The vet exam finds no parasites or serious disease; the diarrhea clears quickly after switching back to the previous food and cutting out dairy. This is a typical diet‑triggered case rather than a major illness.

When it’s serious and needs a vet

  • Diarrhea lasting more than 24–48 hours in kittens or more than a couple of days in adults.
  • Blood in the stool, black/tarry stool, or severe foul smell.
  • Vomiting, refusal to eat, strong lethargy, or signs of pain (crying, hiding, tense belly).
  • Signs of dehydration like dry gums, sunken eyes, or rapid breathing.
  • Known toxin exposure, foreign object ingestion, or existing serious illness (kidney, liver, diabetes, etc.).

In online forums and recent pet‑health articles, diarrhea in cats is a recurring “trending” topic because more people adopt indoor cats, share raw or homemade diets, and discuss gut‑health issues like IBD and microbiome balance. Since the same symptom can mean anything from minor diet upset to a life‑threatening disease, most veterinarians emphasize not guessing at the cause but getting a proper exam, especially if your cat is young, elderly, or acting sick.

TL;DR: What causes diarrhea in cats? Most often diet changes, infections, parasites, stress, inflammatory bowel disease, toxins, medications, foreign objects, or underlying organ disease, and persistent or severe cases should be checked by a vet.

Information gathered from public forums or data available on the internet and portrayed here.