Guides / Cat diarrhea

Cat Diarrhea: Causes and What to Do

Cats / October 2, 2026 / 12 min read / PoopScout Team

You scooped the box and found a puddle instead of a log. Your cat is sitting there looking perfectly normal, and you are wondering whether this is a wait-and-see or a tonight problem. Most of the time it is a wait. Here is how to tell.

What counts as diarrhea in cats?

Diarrhea is poop that is looser, more frequent or larger in volume than your cat's normal. Vets score consistency on a 1 to 7 scale, where 2 is ideal: firm, segmented, easy to scoop. Most cats poop about once a day, so two watery puddles in a morning is a bigger change than one soft log.

Why does my cat have diarrhea? The common causes

The first job is sorting the quick, harmless causes from the ones that need a vet. Vets group them roughly like this.

Food and things they should not have eaten

An abrupt change in diet is the classic trigger. Cornell notes that it can cause diarrhea for a few days on its own, which is why vets ask you to switch foods gradually over a week or more. Table scraps, rich treats, raiding the dog's bowl and licking something off the floor all count too, and a cat who hunts can pick up an upset from the mouse or the parasites that came with it.

Parasites

Parasites are the big one in kittens, outdoor cats and cats from shelters or multi-cat homes. Roundworms and hookworms can cause diarrhea, and kittens pick roundworms up through their mother's milk. Giardia is a microscopic parasite behind diarrhea that comes and goes; Cornell reports it is more common in cats under a year old and in multi-cat households. Coccidia mainly affects kittens, often with mucus in the poop. Tritrichomonas is less familiar: long-running, smelly, cow-pat diarrhea with mucus or blood in young cats, often from catteries, who otherwise stay bright and playful. Routine fecal tests miss it, so your vet may need a special test. Worms you can see in cat poop are a small part of this list, which is why a fecal test matters.

Infections

The one every cat owner should know is feline panleukopenia (feline distemper), a serious virus that causes vomiting and diarrhea, hits kittens hardest, and is the reason kitten vaccines run in a series until about 16 to 20 weeks of age. A kitten, or an unvaccinated cat, with diarrhea plus vomiting or low energy is a vet-now situation.

Diseases outside the gut

Diarrhea that drags on, especially in a middle-aged or older cat, can be a sign of something elsewhere in the body. Cornell lists an overactive thyroid, kidney or liver disease, inflammatory bowel disease (IBD), and lymphoma among the causes of persistent diarrhea. Hyperthyroidism is common in older cats and shows up as weight loss despite a big appetite, thirst, vomiting and diarrhea. IBD causes chronic vomiting, diarrhea and weight loss, and is often managed with a vet-guided diet trial. None of this is worked out at home, so a cat with diarrhea that keeps coming back deserves a proper workup.

Why do cats get diarrhea when nothing has changed?

No obvious culprit is the version that worries people most. A few quiet causes explain most of it.

• Something you did not see. A hunted mouse, a houseplant leaf, a lick of something spilled.
• A parasite that was already there. Giardia and Tritrichomonas can sit quietly and flare.
• Stress you did not clock. A neighbor's cat at the window, a change in your schedule, new furniture. Cats notice.
• A chronic condition starting up. In an older cat, "random" diarrhea that keeps returning is often the first visible sign of thyroid, kidney or bowel disease.
• Medicines. Some drugs loosen poop. If your cat started something new, tell your vet.

Cat has diarrhea but seems fine: wait or call?

If your adult cat has had one or two loose poops, is eating, drinking and their normal self, and there is no blood or vomiting, keep an eye on it for 24 to 48 hours. Keep fresh water available, hold off on new foods and treats, and scoop the box so you can see every poop. Many of these settle on their own.

The watch ends early if anything else shows up: vomiting, a refused meal, blood, a cat who hides or stops grooming, or straining in the box. It ends on schedule if the diarrhea is still there after 24 to 48 hours: Cornell says diarrhea past a day or two with poor appetite, lethargy or vomiting needs a vet as soon as possible, and VCA says more than two days is a call either way. For the gray areas, read cat diarrhea but acting normal.

What cat diarrhea looks like: colors and clues

The look of the poop points your vet in a direction, starting with where in the gut it is coming from.

A small streak of red blood on soft poop usually comes from an irritated colon and is a same-day call, not an emergency, in a cat who is otherwise well. Blood in cat poop and mucus in cat poop have their own guides, and the cat poop color chart covers the rest of the palette.

Diarrhea in cats vs dogs: the cat-only rules

A lot of diarrhea advice online is written for dogs. Cats differ in ways that matter.

• Never give a cat human medicine. Cornell is blunt that some over-the-counter medicines can harm cats, including common remedies for upset stomachs and pain. Ask your vet before giving a cat anything, including products made for dogs.
• Do not fast a cat on your own. Withholding food is common dog advice. Cats who stop eating, especially overweight cats, can develop hepatic lipidosis, a serious liver condition that Cornell says almost always follows a period of not eating. VCA says your vet may advise a short food break or small meals of a gut-friendly diet, and the word that matters is vet.
• A cat refusing food for more than a day is Call your vet today. Even if the diarrhea itself looks mild.
• A cat straining in the box may not be constipated. A cat, especially a male, who strains and passes little or nothing may have a urinary blockage, which can kill within a day or two. If you cannot tell whether it is poop or pee, that is Call a vet now.
• Kittens dehydrate fast. VCA notes that vomiting and diarrhea set kittens up for dehydration quickly. Kitten diarrhea always gets a same-day call at least.

What to feed a cat with diarrhea

Fresh water first: Merck warns that ongoing diarrhea can lead to dehydration and salt imbalances serious enough to cause shock. Then food, kept simple.

1. Do not change food suddenly. If a new food started this, go back to the old one and transition again later, slowly.
2. Small, frequent meals. Several small portions are easier on an irritated gut than one big one.
3. A bland diet only if your vet suggests it. Plain cooked chicken with no skin, bones or seasoning, or a veterinary diet made for gut upsets, are the usual choices. It is a short bridge, not a new diet, so ask your vet how long.
4. No treats or table food. Keep the menu boring until poop is back to normal.
5. Go back gradually. VCA suggests returning to the regular diet over 7 to 10 days once poop is normal.
6. Ask before adding fiber or probiotics. Your vet knows whether they suit your cat.

What to feed a cat with diarrhea goes through the options meal by meal.

What to do today

1. Photograph the poop in good light before you scoop, and note the time and the score.
2. Write down anything new: food, treats, a plant, a trip, a new pet, a medicine.
3. Check your cat, not just the box: eating, drinking, grooming, energy, hiding, vomiting. Check the gums: light rosy pink is normal, pale or white is Call a vet now.
4. Put fresh water out in more than one place, and scoop the box every time so you can see what comes next.
5. Bag a fresh sample and keep it sealed in the fridge, away from food, in case the vet wants it today.
6. Do not give human medicines, dog medicines or home remedies unless your vet says so, and do not fast your cat.

When to call the vet

Call a vet now

• A kitten with diarrhea plus vomiting, low energy, or no interest in food.
• Black, sticky, tar-like poop.
• A lot of fresh blood, or diarrhea that is mostly blood or looks like raspberry jam.
• A cat, especially a male, straining in the litter box with little or nothing coming out.
• Pale or white gums, collapse, or severe weakness.
• Repeated vomiting with belly pain.
• Any chance of rat or mouse bait or another poison, even if your cat seems fine.
• String, thread, yarn, or tinsel hanging from the mouth or bottom. Do not pull it.

Call your vet today

• Diarrhea lasting more than 24 to 48 hours.
• Diarrhea with a poor appetite or a vomit or two, in an adult cat who is still alert.
• Any diarrhea in a kitten, even a bright and playful one.
• A cat who has refused food for more than a day.
• A small streak of fresh blood, or mucus with straining, in a cat who is otherwise well.
• Worms, or rice-like bits, in the poop or on the fur around the bottom.
• Gray, greasy, or pale and bulky poop.
• Diarrhea that keeps coming back, several stool changes in 24 hours, or loose poop with weight loss or thirst in an older cat.
• A cat suddenly pooping or peeing outside the litter box.

Cat diarrhea is usually a short story: a food slip or a stressful day, 24 to 48 hours of watching, and a normal log. The job is to notice when it is not that story, and cats make that harder by hiding how they feel. Watch the box and the cat, keep the cat-only rules in mind, and bring a fresh sample when you go in. The rest of the cat diarrhea guides cover specific situations in more depth. The PoopScout app reads a photo of your cat's poop for score, color and findings and gives you one of these four verdicts.

PoopScout guides are general information for pet owners, written from veterinary sources named above. They are not veterinary advice, they do not diagnose, and they can be wrong for your pet. If your dog or cat seems unwell, or you are worried, call your vet. In an emergency, contact your vet or the nearest emergency animal hospital right away.