Last updated: 26 September 2026
Diarrhoea in cats is usually harmless and passes quickly, for example after a change of food or stress. Take your cat to the vet if it lasts longer than 1–2 days, if the cat is not eating, is lethargic or vomiting, if the stool is bloody or black – and always sooner with a kitten, because kittens dehydrate much faster. Recurring, foul-smelling, pale diarrhoea is often caused by an intestinal parasite such as Giardia. With sudden diarrhoea accompanied by vomiting and lethargy, especially in an unvaccinated kitten, cat parvo (panleukopenia) must also be considered.
In this guide we have gathered the most common causes of diarrhoea in cats, the warning signs, what you can do at home, and when a home rapid test helps.
What counts as diarrhoea?
According to Cornell University's Feline Health Center, a cat has diarrhoea when it passes stool more often than usual and the stool is loose, watery, sometimes an unusual colour (grey, yellow) and smellier than normal. A single softer stool is no cause for concern. What matters is how long it lasts and what other symptoms come with it.
When is diarrhoea in a cat a warning sign?
Call your vet or the emergency service immediately if:
- it is a kitten and, besides the diarrhoea, it is not eating, is listless or vomiting;
- the diarrhoea comes with vomiting and lethargy;
- the stool is bloody, or black and tar-like;
- the cat is not eating, hides, sits hunched, or its belly seems painful;
- you see signs of dehydration: dry, sticky gums, sunken eyes, skin that is slow to return when lifted;
- the diarrhoea lasts longer than 1–2 days or keeps coming back;
- the cat is elderly or chronically ill (for example with kidney or thyroid disease).
Don't wait with a kitten: a small body loses fluid quickly, and diarrhoea can lead to dangerous dehydration within a few hours. In an unvaccinated kitten, sudden vomiting, diarrhoea and lethargy also raise the suspicion of cat parvo, which is an emergency.
The most common causes of diarrhoea in cats
| Cause | What might point to it? | What to do |
|---|---|---|
| Sudden food change, dietary indiscretion | Loose stool for 1–2 days after new food, treats, human food or dairy | Go back to the usual food and switch to the new one gradually. |
| Stress | Temporarily after moving house, travel, a new animal or a vet visit | Calm and observation. If it drags on, an examination. |
| Giardia | Recurring, soft, pale, foul-smelling stool, especially in kittens, shelter cats or multi-cat environments | Stool test; if positive, veterinary treatment and thorough cleaning. |
| Intestinal worms | Diarrhoea, pot belly, poor growth, sometimes visible worms | Discuss deworming with your vet. |
| Cat parvo (panleukopenia) | Sudden onset, vomiting, often bloody diarrhoea, fever, severe lethargy, unvaccinated animal | See a vet immediately. A rapid test helps but does not replace an examination. |
| Chronic diseases | Diarrhoea and weight loss for weeks or months; inflammatory bowel disease, hyperthyroidism, kidney or liver disease, cancer | Veterinary work-up (blood tests, stool examination, ultrasound). |
According to Cornell's overview, causes of diarrhoea in cats include inflammatory bowel disease, intestinal parasites, infections, hyperthyroidism, kidney and liver disease, and panleukopenia. That is why it is not worth guessing when the problem persists.
What can you do at home for mild diarrhoea?
If your cat is an adult, in good spirits, eating and drinking, and has no symptoms other than diarrhoea, in the first 24 hours you can:
- Always provide fresh water. Preventing dehydration is the most important thing. A water fountain encourages many cats to drink.
- Don't starve your cat. In cats, long fasting can be positively harmful. Offer small portions of the usual food, or an easily digestible, gentle food recommended by your vet.
- Don't give human medication. Cornell also warns that some over-the-counter products can be harmful to cats. Never give products containing salicylates (aspirin-type) or paracetamol (acetaminophen), as they are toxic to cats. Only give anti-diarrhoeals or probiotics on your vet's advice.
- Watch the stool and the litter tray. Note how often your cat passes stool, its colour and consistency, and whether there is blood or mucus. This helps your vet a lot.
- Clean often. If an infectious cause is behind it, frequent litter changes and handwashing protect your other animals and your family.
If it does not improve within 24–48 hours, or you see any of the warning signs, don't wait any longer.
When does a home rapid test help?
A rapid test does not replace a vet, but it can help you decide more quickly what to do next. It is especially useful in two situations:
Recurring diarrhoea: Giardia test
If the stool has been fine one day and loose, pale and very smelly the next for weeks, Giardia is one of the most common suspects, especially in kittens, cats from shelters or cats in multi-cat households. The Giardia Ag rapid test detects the parasite's antigen in fresh stool within 5–10 minutes. Because Giardia is shed intermittently, with persistent symptoms a negative test is worth repeating after 2–3 days. Details: Giardia in cats: symptoms, testing, treatment.
Sudden vomiting and diarrhoea in a kitten: FPV test
According to ABCD (European Advisory Board on Cat Diseases), cat parvo (panleukopenia) is fatal in 30–50% of sick cats even with intensive treatment, and the virus remains infectious in the environment for weeks to months. If an unvaccinated or partly vaccinated kitten suddenly develops vomiting, diarrhoea and lethargy, the FPV Ag rapid test gives a result from stool within 5–10 minutes. Set off for the vet in the meantime: in this situation, don't wait for the result. More: Feline panleukopenia (FPV).
Important: according to ABCD, after a live panleukopenia vaccine the vaccine virus can be detectable in the stool for at least 4 weeks and can give a positive test. If your kitten was recently vaccinated, tell your vet. A negative FPV test does not completely rule out infection either, because virus shedding can be intermittent. With symptoms, the vet always decides. We explain how accurate rapid tests are here: How accurate is a home rapid test?
Diarrhoea in kittens: what is different?
- They dehydrate faster, so they need to see a vet sooner.
- They are more sensitive to food changes: after leaving their mother and the breeder, they face new food, a new environment and stress all at once.
- Parasites are more common: Giardia and intestinal worms are most widespread in cats under one year old.
- The vaccination series is not yet complete: according to ABCD, core vaccinations start at 8–9 weeks of age, and the kitten receives the third dose at 16 weeks or older. Until then, protection against panleukopenia is incomplete.
If a new kitten has arrived, it is also worth reading about screening tests: Adopting a cat: what you need to know about screening tests.
What should you bring to the vet?
- a fresh stool sample in a clean, sealable container (as fresh as possible);
- a photo of the stool if the sample is not fresh;
- the timeline of symptoms: when it started, how many times a day the cat passes stool, whether it is eating, whether it is vomiting;
- what it has eaten in the last few days, and whether there was a food change;
- the vaccination record and the date of the last deworming;
- if you did a rapid test at home, the cassette or a photo of the result.
Frequently asked questions about diarrhoea in cats
How long is diarrhoea normal in a cat?
If the cat is otherwise well, eating and playing, mild diarrhoea for a day or two is acceptable. If it lasts longer than 1–2 days, or the cat stops eating, vomits or is lethargic, take it to the vet. With a kitten, don't wait that long.
What can I give my cat for diarrhoea?
Fresh water and small portions of its usual food or a gentle food recommended by your vet. Don't give human medication, as several over-the-counter products are harmful to cats. Only give anti-diarrhoeals or probiotics on your vet's advice.
Why is my cat's stool smelly and pale?
Pale, greasy-looking, very foul-smelling, recurring diarrhoea is typical of small-intestinal problems such as Giardia. A stool examination or Giardia rapid test is worth doing.
Is diarrhoea dangerous in a kitten?
It can be. Kittens dehydrate quickly, and serious infections such as panleukopenia can also cause diarrhoea in them. If your kitten is not eating, is listless or vomiting, take it to the vet immediately.
Can a cat with diarrhoea infect my other cats?
Yes, if an infectious cause is behind it (Giardia, panleukopenia, some viruses or bacteria). Use a separate litter tray, clean often, wash your hands, and discuss with your vet whether your other cats need to be examined too.
Can I find out at home what is causing the diarrhoea?
Partly. Home rapid tests can detect some common infectious causes (Giardia, cat parvo) in stool, but diarrhoea can have many other causes. The test result helps; the diagnosis is made by your vet.
Summary
Mild diarrhoea for a day or two in a cheerful adult cat that is eating usually resolves on its own: fresh water, small portions, observation. Warning signs are vomiting, lethargy, blood in the stool, not eating – and anything that happens in a kitten. With recurring diarrhoea, think of Giardia; with sudden, severe symptoms in an unvaccinated kitten, think of cat parvo. Both can be screened for at home in minutes.
Rapid tests for cats: Giardia, FPV (cat parvo), FIV/FeLV →
From stool or blood, results in minutes, with clear step-by-step instructions.
Sources
- Cornell Feline Health Center: Diarrhea. vet.cornell.edu
- ABCD – European Advisory Board on Cat Diseases: Guideline for Feline Panleukopenia. abcdcatsvets.org
- ABCD – European Advisory Board on Cat Diseases: Guideline for Giardiasis. abcdcatsvets.org
- MancsLab Giardia Ag and FPV Ag instructions for use (with manufacturer's validation data)
Important: this article provides general information and does not replace veterinary advice. With diarrhoea in a kitten, an elderly or sick cat, or if there are warning signs, always contact a vet. MancsLab rapid tests are intended for preliminary screening at home.