Most cat diarrhoea is short-lived and resolves without much intervention. Some of it is a symptom of something that will not.
The useful distinction is not what the diarrhoea looks like but what accompanies it and how long it lasts.
This is orientation for a veterinary conversation rather than a treatment guide.
When to go to a vet
These override any wait-and-see approach.
- Diarrhoea lasting more than about 48 hours in an adult cat.
- Any diarrhoea in a kitten — escalate the same day.
- Blood in the stool, whether fresh red or dark and tarry.
- Vomiting alongside diarrhoea.
- Lethargy, hiding, or refusing food.
- Signs of dehydration — sunken eyes, tacky gums, skin staying tented.
- A cat with a known chronic condition such as kidney disease.
Kittens are the group that catches people out. They have minimal fluid reserves and dehydrate within hours rather than days, so the adult 48-hour guideline does not apply to them.
The common causes
| Cause | Typical picture | Frequency |
|---|---|---|
| Abrupt diet change | Starts within a day or two of new food | Very common |
| Dietary indiscretion | Ate something it should not have | Very common |
| Intestinal parasites | Especially kittens and outdoor cats | Common |
| Bacterial or viral infection | Often with lethargy | Common |
| Stress | New home, new pet, building work | Common |
| Food intolerance or allergy | Recurrent, non-seasonal | Moderate |
| Inflammatory bowel disease | Chronic, often with weight loss | Moderate |
| Hyperthyroidism | With weight loss and big appetite | Older cats |
| Pancreatitis or organ disease | Unwell overall | Less common |
The Merck Veterinary Manual pet owner section covers the differential causes clinically.
Our guides to intestinal worms in cats and hyperthyroidism in cats cover two that are easily missed.
The one that is not diarrhoea
Worth flagging because getting it wrong makes things worse: small amounts of liquid faeces can seep around a hard impaction in a constipated cat.
That is severe constipation presenting as apparent diarrhoea, and treating it as diarrhoea — withholding food, giving anti-diarrhoeal preparations — is actively unhelpful.
The clue is straining and small volumes rather than large loose output. Our guide to constipation in cats covers the distinction.
What the appearance can suggest
Not diagnostic on its own, but it narrows things and is worth describing accurately to a vet.
| Appearance | Often suggests |
|---|---|
| Large volume, watery | Small intestine involvement |
| Small volume, frequent, straining | Large intestine involvement |
| Fresh red blood, small amounts | Large intestine irritation |
| Dark, tarry stool | Bleeding higher up — urgent |
| Mucus present | Colonic inflammation |
| Very pale or greasy | Possible digestive or pancreatic issue |
| Visible worms | Parasites — treat and test |
A photograph is genuinely more useful than a description, and vets are entirely used to being shown one.
Home care for a mild, short episode
For an otherwise well adult cat with mild diarrhoea of under 48 hours.
- Do not withhold food. Prolonged fasting is dangerous in cats.
- Offer a small amount of a bland, easily digestible food more often.
- Ensure water is easily accessible in several places.
- Keep the tray scrupulously clean and note frequency and appearance.
- Do not change the food again mid-episode — that adds a variable.
- Keep the cat indoors so you can monitor output.
The fasting point matters. Our guide to why a cat stops eating covers hepatic lipidosis, which makes withholding food genuinely risky in cats.
What not to give
- No human anti-diarrhoeal medication — several are toxic to cats.
- No milk, which worsens diarrhoea in most cats.
- No leftover antibiotics from a previous episode or another animal.
- No probiotic intended for people without veterinary advice.
- No sudden switch to a different commercial food mid-episode.
Anti-diarrhoeal preparations containing salicylates are particularly dangerous for cats. This is not an area to improvise in.
Chronic and recurrent diarrhoea
Diarrhoea that keeps returning, or never fully resolves, is a different problem from a one-off upset.
Chronic cases usually need investigation: faecal testing, bloodwork, sometimes imaging or a diet trial. Inflammatory bowel disease, food intolerance and parasites account for a large share.
Recurrent diarrhoea with weight loss deserves particular urgency, since that combination points toward chronic disease rather than a passing upset.
Our guide to food allergy and elimination diets covers the diet trial approach, which is the same method used for digestive signs.
Kittens and newly adopted cats
Both groups get diarrhoea frequently, and for overlapping reasons: parasites, stress, and a diet change all at once.
Keep the shelter’s food for the first fortnight rather than changing immediately, ensure worming is up to date, and give the cat a quiet settling-in space.
Our guides to the first 30 days with a new cat and caring for very young kittens cover both situations.
Hygiene
Some causes of feline diarrhoea are transmissible, to other cats and occasionally to people.
Wash hands after handling the tray, scoop promptly, disinfect the tray, and keep an affected cat separate from others in the household until a cause is known.
Our guide to hygiene around cats covers the zoonotic side in more detail.
Feeding through a bout
What you feed during and after an episode affects how quickly the gut settles.
Withholding food for long periods is no longer standard advice for cats. Cats that stop eating for more than a day or two risk hepatic lipidosis, a serious liver complication that is far worse than the original problem.
- Keep offering small, frequent meals rather than one large one.
- A plain, highly digestible food is easier than a rich one — a veterinary gastrointestinal diet if you have one.
- Reintroduce the normal food gradually over three to five days once stools firm up.
- Keep water available everywhere, and consider adding water to wet food.
- Avoid new treats, dairy and table food until things have been normal for a week.
If the cat refuses food entirely for more than 24 hours, that is a reason to call the vet regardless of what the stools are doing. Our guide to choosing a vet covers having that relationship in place before you need it.
Frequently Asked Questions
How long can cat diarrhoea last before I worry?
About 48 hours in an otherwise well adult cat. Any diarrhoea in a kitten needs same-day attention, as does diarrhoea with blood, vomiting, lethargy or signs of dehydration.
Should I withhold food from a cat with diarrhoea?
No. Prolonged fasting risks hepatic lipidosis, a serious liver condition. Offer small amounts of bland, easily digestible food more frequently rather than starving the cat.
Can I give my cat human anti-diarrhoeal medication?
No. Several are toxic to cats, particularly preparations containing salicylates. Never use human medication, leftover antibiotics or a dog product without veterinary direction.
My cat is passing small amounts of liquid — is that diarrhoea?
Possibly not. Liquid seeping around a hard impaction is severe constipation, and treating it as diarrhoea makes it worse. Straining with small volumes points that way rather than to diarrhoea.
Why does my newly adopted cat have diarrhoea?
Usually a combination of stress, a diet change and parasites all arriving at once. Keep the shelter’s food for the first fortnight, confirm worming is current, and give the cat a quiet settling space.
When does recurrent diarrhoea need investigating?
When it keeps returning or never fully resolves, and especially alongside weight loss. Chronic cases usually need faecal testing, bloodwork and sometimes a diet trial or imaging.