Diarrhea is one of the most common reasons cats end up at the vet, and one of the most worrying things to find in the litter box. The good news: a single soft stool in an otherwise happy, eating cat is rarely an emergency. The important part is knowing which signs mean “watch and wait” and which mean “call now.” This guide walks through both, with honest, practical advice grounded in veterinary sources like the Cornell Feline Health Center and the Merck Veterinary Manual.
What counts as diarrhea?
Diarrhea simply means stool that is looser or more watery than normal, often passed more frequently or with more urgency. You might also notice accidents outside the litter box, straining, or mucus. It can range from a one-off soft pile to repeated watery messes.
It helps to sort it by time course:
- Acute diarrhea comes on suddenly and is usually short-lived — a day or two. It is often tied to something recent, like a diet change or a snack the cat shouldn’t have had.
- Chronic diarrhea lasts about three weeks or longer, or keeps recurring. Chronic diarrhea always deserves a proper veterinary workup, because it points to an underlying condition rather than a passing upset.
If diarrhea comes alongside vomiting, the combination raises the stakes — a cat can lose fluid quickly from both ends. Our guide on why your cat is vomiting covers that side of things.
Common causes
Diarrhea is a symptom, not a diagnosis. Many different things can trigger it, and the clues that come with it often hint at the cause. Use the table below as a starting point — not a substitute for a vet’s assessment.
| Cause | Clues | What to do |
|---|---|---|
| Diet changed too fast | Started within a day or two of switching food | Slow the transition over 7-10 days (the same gradual principle in our food-switching guide) |
| Dietary indiscretion (scavenging, treats, garbage) | Got into something new; otherwise bright | Remove access; monitor for 24-48 hours |
| Food intolerance or allergy | Recurs with a specific food; sometimes itchy skin | Discuss a diet trial with your vet |
| Intestinal parasites (worms, giardia, coccidia) | Common in kittens; may see worms or mucus | Vet fecal test and dewormer; especially key for new kittens (see the new kitten checklist) |
| Viral or bacterial infection | Often with fever, lethargy, poor appetite | Veterinary exam; can be serious in kittens |
| Inflammatory bowel disease (IBD) | Chronic, waxing and waning, weight loss | Vet workup needed for diagnosis |
| Hyperthyroidism | Older cats; weight loss despite big appetite | Vet bloodwork |
| Stress or anxiety | New home, travel, household changes | Reduce stressors; monitor |
| Toxins or poisonous plants/foods | Sudden, may have vomiting or drooling | Call ASPCA Animal Poison Control (888) 426-4435; see foods toxic to cats |
A note on kittens: diarrhea is more dangerous in young animals. They have small fluid reserves and dehydrate fast, so what would be a “wait and see” in an adult is often a “see the vet today” in a kitten.
Red flags — see the vet promptly or urgently
Call your veterinarian (or an emergency clinic) right away if you notice any of these:
- Blood in the stool — bright red streaks, or black, tarry stool (which suggests bleeding higher up).
- Diarrhea lasting more than about 24-48 hours, or chronic diarrhea of three weeks or more.
- A kitten, a senior cat, or a cat with an existing illness — these cats have far less margin for error.
- Profuse or watery diarrhea, which drains fluid quickly.
- Signs of dehydration or lethargy — sunken eyes, tacky gums, weakness, hiding.
- Your cat stops eating. A cat that won’t eat is at real risk of hepatic lipidosis (fatty liver); see why your cat isn’t eating.
- Vomiting on top of the diarrhea, a painful or bloated belly, or obvious distress.
- A suspected toxin or plant ingestion — call ASPCA Animal Poison Control at (888) 426-4435.
When in doubt, a phone call to your vet costs nothing and often saves a lot of worry.
Safe home care for a mild case
If your cat is an otherwise bright, playful adult with mild, recent diarrhea and none of the red flags above, you can reasonably monitor at home for a day or two.
Do:
- Keep water available and encourage drinking. Wet food and a clean, full bowl help. Hydration is the main thing you are protecting against.
- Offer an easily digestible, bland diet for a short stretch — ideally one your vet recommends. Small, frequent portions are gentler than a big meal. Once stools firm up, transition back to the normal food gradually.
- Keep the litter box clean and watch what comes out. Note the color, consistency, frequency, and any blood or mucus — this is exactly the detail your vet will ask about.
- Monitor energy and appetite. A cat that stays bright and keeps eating is reassuring; any slide toward listlessness or refusing food changes the plan.
Don’t:
- Don’t fast your cat. This is a key difference from dogs. Cats should not go without food, because even a day or two of not eating can trigger fatty liver disease. Keep offering small amounts.
- Don’t give human anti-diarrheal medicine. Products containing bismuth or salicylates (the aspirin-like ingredient in Pepto-Bismol) can be toxic to cats, and other over-the-counter remedies can be dangerous or mask serious illness. Medications are a vet-only decision.
- Don’t ignore worsening signs. If things aren’t clearly improving within 24-48 hours, escalate to your vet.
Prevention
You can’t prevent every bout, but you can lower the odds:
- Make diet changes gradually over a week or more rather than overnight. Portioning consistently helps too — our feeding calculator and how-much-to-feed guide can keep meals steady.
- Stay current on parasite prevention and routine fecal checks, especially for kittens and outdoor cats.
- Keep toxins, human foods, and unsafe plants out of reach. Our food safety checker helps you check whether something is safe before your cat gets to it.
- Reduce stress around moves, travel, new pets, and household upheaval.
When to call the vet — and a disclaimer
Trust your instincts. A single soft stool in a happy, hungry cat is usually nothing. Blood, a poorly cat, a kitten or senior, a cat that stops eating, or diarrhea that drags on past a day or two all warrant a professional opinion.
This guide is educational and not a substitute for veterinary care. Cats are very good at hiding illness, and diarrhea can be the visible tip of a more serious problem. When you are unsure, contact your veterinarian or an emergency clinic. For a suspected poisoning, call the ASPCA Animal Poison Control Center at (888) 426-4435 right away.