Why cats get diarrhea
PetMD is blunt: diarrhea is a symptom, never a disease, and never normal. The cause list spans the harmless-to-deadly range, so the job at home is sorting where yours sits.
The six families of acute diarrhea (under 14 days): infections (parasites, bacteria, viruses), inflammation (food allergy), metabolic or endocrine disease (diabetes, hyperthyroidism), cancer, obstruction, and poisoning. Treats and sudden diet changes sit on top of all six — contaminated product, too-fast introduction, toxic ingredients or an allergy (PetMD).
Anything running two to three weeks or longer is chronic by definition, and PetMD's chronic list shifts toward conditions that need long-term management: IBD, resistant infections, food allergy, hyperthyroidism, kidney disease, liver disease, diabetes, pancreatitis and GI lymphoma.
Reading the litter box
What you see narrows the cause list considerably (PetMD):
- Bloody stool — always concerning. Dark red or black means upper-GI bleeding (stomach, small intestine); bright red or coating means lower tract (colon, rectum). Either way, vet visit.
- Mucus coating — suggests inflammation, dehydration or parasitic infection.
- Liquid stool — dehydrates and malnourishes quickly; more serious than soft-but-formed.
- Yellow or green — sometimes what she ate (grass, green treats), but can signal gallbladder disease; pure yellow stool can be an emergency tied to liver disease, zinc poisoning, immune-mediated hemolytic anemia or bacterial overgrowth.
- Volume and frequency — large-volume points to the small bowel; frequent small volumes with straining point to the large bowel (PetMD, chronic-diarrhea guide).
The combination that skips the appointment
One rule outranks everything else on this page: vomiting plus diarrhea in a cat is always an emergency (PetMD). The possible causes behind it are the serious list — intestinal obstruction, toxin ingestion, organ failure such as kidney disease, pancreatitis, diabetic ketoacidosis, Addisonian crisis, severe infection, severe food allergy.
Also go now for: blood in the stool, black tarry stool, a lethargic cat, suspected poisoning, or a kitten with diarrhea — small bodies dehydrate dangerously fast. If anything is hanging from the rectum after a bowel movement, don't pull it; call the vet (PetMD).
The 24-hour rule and what to bring
If diarrhea hasn't resolved within 24 hours, PetMD says seek veterinary care — and lower that bar for kittens, senior cats, cats with chronic disease and pregnant cats, who carry higher risk from complications.
Before the visit (PetMD):
- Photograph the stool — color and consistency are diagnostic gold.
- Keep water available — hydration is the battleground; don't withhold food unless your vet directs it.
- Don't reach for human medication — no over-the-counter anti-diarrheals unless your veterinarian says so.
- Reconstruct the last few days — new food, new treats, table scraps, plants, medication changes, possible toxin access.
- Save a sample if you can — a stool bag is genuinely useful for the fecal test.
Expect a physical exam checking hydration and abdominal comfort, then likely bloodwork, urinalysis and a fecal test. Chronic cases add imaging, endoscopy or biopsies. Treatment follows the cause — probiotics and B12 for gut support, elimination or hydrolyzed-protein diets for suspected food allergy, and targeted therapy for organ disease (PetMD).
Frequently asked questions
How long does cat diarrhea last before I should worry?
If it isn't self-resolving within 24 hours, PetMD says seek veterinary care — sooner for kittens, seniors, pregnant cats and cats with chronic disease. Anything past 24–48 hours with other signs also warrants a visit.
Why is my cat’s poop soft but not liquid?
Soft-but-formed stool is generally less severe than liquid and suggests a short-term digestive upset (PetMD). It still deserves monitoring — and a vet if it persists past a day or two, or comes with other signs.
My cat has diarrhea and vomiting. What do I do?
Treat it as an emergency and contact your vet now. Vomiting combined with diarrhea can indicate intestinal obstruction, toxin ingestion, organ failure, pancreatitis or diabetic ketoacidosis (PetMD).
Can a sudden food change cause diarrhea?
Yes. Treats and new foods can trigger diarrhea when they're contaminated, introduced too fast, or contain something toxic or allergenic (PetMD). Transition new food gradually, and if the diarrhea started with a switch and resolves on its own, still worth mentioning at the next checkup.