Why does my dog or cat have diarrhoea?
One or two loose stools in a bright, active pet can often be watched at home.
Most sudden diarrhoea in an otherwise well adult settles within a day or two with simple care. Contact a vet the same day — or go to emergency — if you see any of these:
- Watery or repeated diarrhoea with vomiting, or your pet can't keep water down
- Blood in the stool, or black, tarry stool
- A dull, weak or collapsed pet, or signs of dehydration (tacky gums, skin that stays tented)
- A puppy, kitten, senior, pregnant or unwell pet — or a cat whose diarrhoea lasts beyond a day
Diarrhoea is a sign, not a disease. In a healthy adult dog or cat, a short bout is usually mild and often settles within 24–48 hours with rest and a bland diet. What matters more than the exact cause is how your pet is coping: blood, black tarry stool, repeated vomiting, weakness, dehydration, or a very young, old or unwell pet all mean it's time to call your vet.
- A short bout in a bright adult often settles in a day or two.
- Blood, black tarry stool, duration and your pet's overall state matter most.
- Never give human anti-diarrhoea medicines (loperamide, bismuth) unless your vet directs — some are risky, especially for cats.
- Keep water available; dehydration is the real danger. A fresh stool sample helps your vet.
What diarrhoea means
Diarrhoea is loose, watery or more-frequent stool caused by faster movement through the gut, reduced water absorption, or inflammation of the intestine. Vets describe it as acute (sudden, usually under two weeks) or chronic (lasting around three weeks or more), and as coming from the small or large bowel — the pattern helps point to the cause.
Colour and consistency can hint at the origin: fresh red streaks tend to come from the lower bowel, while black, tarry stool can mean digested blood from higher up and is more concerning. Most single episodes in a well pet are self-limiting, but the picture changes quickly in the very young, very old, or already-ill.
Common causes to consider
These are categories a vet thinks through — not a diagnosis of your pet:
- Dietary — a sudden food change, rich or fatty food, or scavenging on a walk.
- Parasites — worms or protozoa such as Giardia, common in young animals.
- Infections — viral or bacterial gut infections (parvovirus in unvaccinated puppies is serious).
- Stress — travel, boarding or routine changes can upset the gut.
- Medication-related — some drugs, including after a course of antibiotics.
- Chronic GI disease — food-responsive disease or inflammatory bowel disease, where diarrhoea recurs.
- Something serious — a blockage or systemic illness, where diarrhoea is one of several signs.
Dogs vs cats
Dogs scavenge and eat things they shouldn't far more than cats, so dietary and infectious causes are common. Cats are fussier eaters, so external triggers are less frequent — which means diarrhoea in a cat, especially alongside not eating, deserves a lower threshold for a vet visit. In both species, puppies and kittens dehydrate very quickly and should be seen sooner rather than later.
Three things come up often in Indian homes. In the monsoon, contaminated water and a rise in gut infections mean diarrhoea deserves a lower threshold for a vet visit. Scavenging on walks — street food, discarded bones, bin raids — is a frequent trigger. And a background parasite burden makes routine deworming (on your vet's schedule) worthwhile. In the heat, a pet with diarrhoea dehydrates faster, so keep water available and act sooner. Some causes, such as Giardia, can pass to people — wash hands and clean up promptly.
What to check, and what you can safely do
Before and during a vet call, it helps to note:
- How many episodes, and over how long
- Watery or just soft; any mucus
- Colour — fresh red blood, or black and tarry
- Whether there is vomiting too
- Energy, appetite and drinking
- Gum moisture and whether pinched skin springs back (dehydration)
- Any recent food change, scavenging, new medicine or stress
Safe to do
- Keep fresh water available at all times.
- Offer small amounts of a bland diet — plain boiled rice with a little plain chicken — for a short period if your vet agrees.
- Keep the litter tray or yard area clean so you can monitor each stool.
- Deworm on the schedule your vet recommends.
- Save a fresh stool sample (less than a few hours old) to bring for faecal testing.
Do not
- Give human anti-diarrhoea medicines (loperamide/Imodium, Pepto-Bismol) — some contain aspirin-type ingredients that can be dangerous, especially to cats.
- Withhold water.
- Make sudden diet changes — switch foods over 5–7 days.
- Wait it out if there is blood, black stool, or a flat, weak pet.
- Share medicines between pets or reuse leftover prescriptions.
When to see a veterinarian
Monitor / routine: one or two soft stools in a bright pet that is eating and drinking — watch for 24–48 hours with a bland diet.
Same day: diarrhoea lasting beyond 24–48 hours, repeated vomiting, blood or black tarry stool, low energy or poor appetite, a puppy, kitten, senior, pregnant or chronically-ill pet — or any cat that is also not eating.
Emergency: profuse watery or bloody diarrhoea with weakness or collapse, clear signs of dehydration, a bloated or painful belly, or a suspected toxin or parvovirus.
What the vet may check
Your vet will start with your history and an examination, including checking hydration, then decide what's needed — often a faecal test for parasites, and sometimes blood tests or imaging. Treatment depends on the cause and may include a bland or therapeutic diet, deworming or fluids. This page doesn't give medicine names or doses; those decisions belong with your vet.
Frequently asked questions
How long is too long for diarrhoea?
In a bright adult, a day or two of mild diarrhoea can often be watched. Beyond 24–48 hours, or sooner if there is blood, vomiting, weakness or dehydration, call your vet. Puppies, kittens, seniors and any cat that is also off food should be seen sooner.
Can I give my pet Imodium or Pepto-Bismol?
Not on your own. Human anti-diarrhoea medicines can be unsafe for pets — some contain aspirin-type ingredients that are especially risky for cats. Only ever use them if your own vet specifically directs it.
There's a little blood in the stool — is that an emergency?
A small streak of fresh blood with an otherwise well pet is worth a same-day call rather than a panic. But black, tarry stool, or blood with weakness, repeated vomiting or a painful belly, should be treated urgently.
My pet has diarrhoea and is vomiting — is that worse?
The two together raise the risk of dehydration and can point to something needing treatment, so it warrants a prompt vet contact — sooner in the very young, very old, or already-unwell.
Could food have caused it?
Often, yes — a sudden change of diet, rich or fatty food, or scavenging are among the most common triggers. Introduce new foods gradually over 5–7 days.
Is my pet's diarrhoea contagious to me?
Some causes, such as certain parasites and bacteria, can pass to people. Wash your hands after handling stool, clean up promptly, and mention any human tummy upsets to your doctor.
Sources
- SourceMerck Veterinary Manual — Colitis in Small Animals (2025). merckvetmanual.com
- SourceMerck Animal Health — Dealing with diarrhoea in pets. merck-animal-health-usa.com
- SourceRoyal Veterinary College / VetCompass — Acute diarrhoea in dogs under UK primary care. ncbi.nlm.nih.gov