Symptom guide

Why Does My Cat Have Diarrhea? Causes and Care

What causes diarrhea in cats, from diet changes and stress to parasites, IBD and hyperthyroidism, what you can do at home and when your cat needs a vet.

Updated October 2026 · 6 min read · By the Hushku editorial team · 3 sources

See a vet within 24 hours. Vet if it lasts over 1–2 days or your cat is unwell

Short answer

Mild diarrhea in an adult cat that's bright and eating can be caused by a diet change or stress and may settle within a day or two. Cornell Feline Health Center advises seeing a vet if it lasts more than a day or two, or comes with poor appetite, lethargy or vomiting. Kittens, older cats and cats with blood in the stool should be seen sooner.

Key facts

Cornell advises a vet visit if diarrhea lasts more than a day or two.
See a vet sooner with vomiting, poor appetite or lethargy.
Many adult cats can't digest lactose, so milk causes diarrhea.
Never give human anti-diarrhea medicines to cats.

This guide is general information, not a diagnosis. If your pet seems unwell, or you're worried, call your vet.

Overview

Diarrhea happens when stool moves through the intestines too quickly to absorb enough water, nutrients and electrolytes. Short bouts are often caused by a sudden diet change, stress such as a car journey or boarding, or kittens adjusting to solid food.

In adult cats, diarrhea that isn't linked to diet is often caused by inflammatory, infectious or tumour-related disease in the gut, and problems elsewhere in the body, such as hyperthyroidism and kidney or liver disease, can cause it too.

Note the details: how often, how much, the colour, whether there's mucus or blood, and whether your cat is straining. A photo helps your vet.

Go to a vet now if you see

Diarrhea in a young kitten, especially with vomiting or lethargy
Large amounts of blood, or black tarry stools
Vomiting as well as diarrhea, or refusing food
Weakness, collapse, or sunken eyes and sticky gums (dehydration)
Possible poisoning, such as lilies or human medicines

Common causes

1. Sudden diet change or new treats
Usually mild
Usually short-lived. Switch foods gradually over at least a week.
2. Milk and dairy
Usually mild
Many adult cats can't digest lactose, so milk causes diarrhea.
3. Stress
Usually mild
Travel, boarding, a new pet or a move can upset the gut.
4. Parasites
Needs a vet
Roundworms, hookworms, giardia and coccidia are common in kittens and outdoor or shelter cats.
5. Infections
Serious
Bacterial and viral infections, including panleukopenia in unvaccinated kittens, which is life-threatening.
6. Food intolerance or allergy
Needs a vet
Recurring diarrhea, sometimes with vomiting or itchy skin.
7. Inflammatory bowel disease and lymphoma
Serious
Ongoing diarrhea and weight loss in middle-aged and older cats.
8. Hyperthyroidism
Serious
Diarrhea or vomiting with weight loss and a big appetite in older cats.

What you can do at home

Make sure fresh water is always available; wet food helps with hydration.
Don't withhold food from cats for long; offer small meals of their usual food or a vet gastrointestinal diet.
Don't give human anti-diarrhea medicines; some are toxic to cats.
Keep the litter box extra clean and wipe your cat's bottom if needed.
Collect a fresh stool sample for your vet.

When to see a vet

Diarrhea lasting more than a day or two
Diarrhea with poor appetite, lethargy or vomiting
Blood or lots of mucus in the stool
Recurring bouts, or weight loss

Prevention

Change foods gradually
Don't feed cow's milk
Keep up with deworming and vaccines
Wash food bowls daily and avoid feeding raw meat, which can carry harmful bacteria

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Sources

We check guides against veterinary sources and update them when guidance changes. How we write and review.

Questions.

Can hairballs cause diarrhea?

Not usually. Hairballs mainly cause vomiting or, rarely, constipation or a blockage.

Is pumpkin good for cat diarrhea?

A small amount of plain cooked pumpkin adds fibre and helps some cats, but it doesn't treat the cause. See your vet if diarrhea continues.

Can indoor cats get worms?

Yes. Eggs can come in on shoes, and cats can be infected by eating insects or rodents, or from fleas (tapeworm).

Key facts

Overview

Go to a vet now if you see

Common causes

1. Sudden diet change or new treats

2. Milk and dairy

3. Stress

4. Parasites

5. Infections

6. Food intolerance or allergy

7. Inflammatory bowel disease and lymphoma

8. Hyperthyroidism