Cat Diarrhea: Causes and When It's Serious

Diarrhea in cats often traces back to something dietary — a sudden food change, a new treat, dairy (which most adult cats don't tolerate well), or getting into something outside their normal diet. In indoor-outdoor cats, intestinal parasites are also a common and frequently overlooked cause, since infestations aren't always visually obvious.

Chronic or recurring diarrhea — happening on and off over weeks or months rather than a single short episode — points toward a different category of causes worth actually investigating: inflammatory bowel disease, food sensitivities or allergies, hyperthyroidism in older cats, or less commonly, more serious conditions. Cats are also good at hiding how unwell they feel, so a cat with chronic diarrhea might otherwise seem largely normal in energy and behavior, which can make owners underestimate the significance of the ongoing symptom.

Red flags: diarrhea lasting more than a couple of days, diarrhea with blood or mucus, diarrhea combined with vomiting, weight loss, or decreased appetite, or diarrhea in a kitten (who dehydrates much faster than an adult cat).

What to do: A single, mild, short episode in an otherwise normal-acting adult cat is often reasonable to monitor for a day or two with a bland or easily digestible diet. Diarrhea that persists, recurs regularly, or comes with any of the red flags above is worth a proper vet visit, including a fecal test to check for parasites — a step that resolves a surprising number of "mystery" cat diarrhea cases.

For a related account of when ongoing digestive symptoms in a cat turned out to be more significant than expected, here's a full story of what extended vomiting looked like for one cat.