Cat Diarrhoea: Causes, Home Treatment & When to See a Vet

Diarrhoea in cats is one of those symptoms that ranges from completely benign to genuinely concerning, and knowing the difference can be difficult for owners. A single bout of soft stool after eating something unusual is rarely cause for alarm. But diarrhoea that lasts more than 24 hours, contains blood, or is accompanied by other symptoms like vomiting or lethargy requires veterinary attention.

As a vet, I see cats with diarrhoea every single day. The vast majority of cases are mild and self-limiting, but a small proportion are caused by serious underlying conditions that require investigation and treatment. This guide will help you work out which category your cat falls into and what to do about it.

What Is Normal Cat Faeces?

Healthy cat faeces should be firm but not hard, brown in colour, and formed into discrete logs. It should hold its shape when you scoop the litter tray, and while it won't smell pleasant, it shouldn't be overwhelmingly offensive.

Diarrhoea is loose, watery, or unformed stool. It can range from slightly soft to completely liquid, and the frequency of defecation usually increases. The colour, consistency, and presence of blood or mucus all provide important clues about what's causing it.

Common Causes of Diarrhoea in Cats

1. Dietary Indiscretion

The most common cause of acute diarrhoea in cats is eating something they shouldn't have. This might be human food, spoiled food from the bin, a dead animal they caught outside, or simply eating too much too quickly. Dietary indiscretion usually causes a single episode or a day of loose stools that resolves on its own.

2. Sudden Diet Change

Switching foods too quickly is a frequent cause of diarrhoea. Cats have sensitive digestive systems, and even a change from one high-quality food to another can trigger upset if done abruptly. Always transition foods gradually over 7-14 days.

3. Food Intolerance or Allergy

Some cats develop sensitivities to specific proteins or ingredients in their food. Food intolerance typically causes chronic, intermittent diarrhoea rather than a sudden acute bout. Common culprits include beef, dairy, fish, and certain grains. An elimination diet under veterinary guidance is the best way to identify the trigger.

4. Intestinal Parasites

Worms (roundworms, tapeworms, hookworms) and protozoal parasites (Giardia, Coccidia, Tritrichomonas) are common causes of diarrhoea, particularly in kittens and outdoor cats. You may see worms in the faeces, or the stool may simply be persistently loose. Regular parasite treatment is essential for all cats.

5. Inflammatory Bowel Disease (IBD)

IBD is a chronic condition where the walls of the intestine become infiltrated with inflammatory cells. It causes persistent or intermittent diarrhoea, often with mucus, alongside weight loss, vomiting, and variable appetite. Diagnosis requires intestinal biopsies, and management involves dietary modification and immunosuppressive medication.

6. Infections

Bacterial infections (Salmonella, Campylobacter, Clostridium), viral infections (feline parvovirus, coronavirus), and fungal infections can all cause diarrhoea. Kittens are particularly vulnerable. Infectious diarrhoea is often accompanied by fever, lethargy, vomiting, and rapid deterioration.

7. Pancreatitis

Inflammation of the pancreas commonly causes diarrhoea alongside vomiting, abdominal pain, and lethargy. Pancreatitis can be acute or chronic and ranges from mild to life-threatening. Diagnosis requires blood tests and ultrasound.

8. Hyperthyroidism

An overactive thyroid gland is very common in older cats and often causes increased appetite, weight loss, hyperactivity, and diarrhoea. It's easily diagnosed with a blood test and very manageable once treated. For more on hyperthyroidism symptoms, read our detailed guide on signs of an overactive thyroid.

9. Kidney Disease

Chronic kidney disease can cause diarrhoea due to the build-up of toxins in the bloodstream and changes in gut bacteria. Other signs include increased thirst and urination, weight loss, and poor appetite.

10. Stress and Anxiety

Stress is an underestimated cause of diarrhoea in cats. Moving house, a new pet, changes in routine, or even a dirty litter tray can trigger stress-related diarrhoea. It usually resolves once the stressor is removed.

When Is Cat Diarrhoea an Emergency?

Seek immediate veterinary care if your cat:

• Has bloody diarrhoea (bright red or dark, tarry stools)
• Is vomiting repeatedly alongside diarrhoea
• Is lethargic, unresponsive, or collapsed
• Has not eaten or drunk for more than 24 hours
• Is showing signs of dehydration: sunken eyes, dry gums, skin tenting when pinched
• Has a high fever (over 39.5°C / 103°F) read our guide on normal cat body temperature
• Is a kitten: young cats deteriorate rapidly
• Has profuse watery diarrhoea that won't stop

For more on recognising serious illness, read our guide on how to tell if your cat is in pain and our overview of cat illness symptoms and when to act.

Home Treatment for Mild Cat Diarrhoea

If your cat has had one or two episodes of soft stool but is otherwise well eating, drinking, alert, and playful you can initially manage at home:

• Withhold food for 12-24 hours (water should always be available) to give the gut time to rest
• Reintroduce food gradually with small, frequent meals of bland food (plain boiled chicken, white fish, or a prescription gastrointestinal diet)
• Ensure fresh water is always available cats with diarrhoea dehydrate quickly
• Keep the litter tray clean to monitor stool consistency and frequency
• Monitor closely if diarrhoea persists beyond 24 hours, or your cat seems unwell, call your vet

Do not give human anti-diarrhoeal medications like Imodium or Pepto-Bismol to cats they can be toxic.

What Does the Colour and Consistency Mean?

• Yellow or orange diarrhoea: Often indicates food moving too quickly through the intestines; can also suggest liver or pancreatic issues
• Green diarrhoea: May indicate bacterial infection or bile passing through too quickly
• Black, tarry stools: Suggests digested blood from the upper GI tract (stomach, small intestine); requires immediate vet attention
• Bright red blood: Indicates bleeding in the lower intestines or rectum; requires same-day vet attention
• Mucus in stool: Suggests inflammation of the large intestine (colitis)
• Watery, explosive diarrhoea: Often infectious or toxic cause; risk of rapid dehydration

How Litter Sense Helps You Monitor Digestive Health

Some of the conditions that cause chronic diarrhoea particularly kidney disease, hyperthyroidism, and inflammatory bowel disease also affect the urine. Litter Sense monitors your cat's urine daily and can flag early changes that suggest an underlying problem is developing, giving you the chance to act before symptoms become severe.

To learn more about how Litter Sense works, read our complete guide on how Litter Sense monitors cat health.

Frequently Asked Questions

How long should cat diarrhoea last?

A single episode or one day of loose stools is not unusual and often resolves on its own. If diarrhoea lasts more than 24 hours, or if your cat seems unwell, contact your vet. Chronic diarrhoea (lasting more than a week) always requires investigation.

Can I give my cat anything for diarrhoea?

Do not give human anti-diarrhoeal medications. Your vet may prescribe probiotics, anti-inflammatories, antibiotics, or other treatments depending on the cause. Never medicate your cat without veterinary advice.

Should I withhold food if my cat has diarrhoea?

For mild, acute diarrhoea, withholding food for 12-24 hours (with water always available) can help the gut rest. Reintroduce bland food gradually. If diarrhoea persists or your cat seems unwell, see your vet.

Why does my cat have diarrhoea but is acting normal?

Mild dietary upset, stress, or food intolerance can cause diarrhoea without affecting overall demeanour. If your cat is eating, drinking, and acting normally, you can monitor at home for 24 hours. If diarrhoea continues beyond this, see your vet.

Can stress cause diarrhoea in cats?

Yes. Cats are sensitive to environmental changes, and stress from moving house, new pets, or changes in routine can trigger diarrhoea. It usually resolves once the stressor is removed.

Is cat diarrhoea contagious to humans?

Some causes of cat diarrhoea (Salmonella, Campylobacter, Giardia) are zoonotic and can spread to humans. Always wash your hands thoroughly after handling the litter tray, especially if your cat has diarrhoea.