Understanding where the diarrhea originates helps determine the cause and urgency:
Small bowel (small intestine) diarrhea:
- Large volume of watery stool
- Normal or decreased frequency (2–4 times per day)
- May contain undigested food or fat
- No straining or urgency
- If chronic, often leads to weight loss
- Causes: food intolerance, IBD, lymphoma, parasites, pancreatitis
Large bowel (colon) diarrhea:
- Small amounts of soft or mucous stool
- Increased frequency (5–10+ times per day)
- Straining and urgency (may have accidents outside the litter box)
- May contain fresh blood or mucus
- Weight loss less common
- Causes: colitis, parasites (especially Tritrichomonas), stress, dietary indiscretion
Many cats have mixed pattern diarrhea involving both small and large bowel signs, which can make diagnosis trickier.
Common Causes of Diarrhea in Cats
Dietary Causes
Sudden food change — one of the most common causes. Cats have sensitive digestive systems, and abrupt diet switches can trigger diarrhea that lasts 3–7 days. Always transition food gradually over 7–10 days.
Food intolerance or allergy — chronic or recurring diarrhea can indicate sensitivity to specific proteins. Common allergens include beef, fish, dairy, and chicken. Unlike true allergies, intolerances don't involve the immune system but still cause GI upset.
Dietary indiscretion — eating something unusual: table scraps, garbage, plants, insects, or even hairbands and string.
Lactose intolerance — most adult cats are lactose intolerant. Milk, cream, and cheese can cause diarrhea. Despite the popular image, cats should not be given cow's milk.
Intestinal parasites — extremely common, especially in kittens and outdoor cats:
- Roundworms and hookworms — transmitted from mother to kittens or through the environment
- Giardia — protozoal parasite causing intermittent watery diarrhea
- Coccidia — common in young kittens from shelters or breeders
- Tritrichomonas foetus — protozoal infection causing chronic large bowel diarrhea, especially in young cats from multi-cat environments
Feline panleukopenia (feline parvovirus) — severe, often fatal viral disease in unvaccinated cats. Causes severe bloody diarrhea, vomiting, high fever, and rapid dehydration.
Coronavirus (feline enteric coronavirus) — common and usually mild. Not to be confused with FIP (a rare mutation of the same virus that causes a completely different, serious disease).
Bacterial infections — Salmonella, Campylobacter, Clostridium. Raw-food diets increase the risk.
Chronic Diseases
Inflammatory bowel disease (IBD) — chronic inflammation of the intestinal lining. One of the most common causes of persistent diarrhea in adult cats. Diagnosis requires intestinal biopsy or, increasingly, response to treatment trials.
Hyperthyroidism — overactive thyroid in senior cats. Increases gut motility, causing diarrhea, weight loss despite good appetite, and increased activity.
Chronic kidney disease — common in older cats. Can cause GI upset including diarrhea, nausea, and decreased appetite.
Intestinal lymphoma — the most common cancer in cats. Low-grade lymphoma can cause chronic diarrhea and weight loss. Diagnosis requires biopsy.
Pancreatitis — inflammation of the pancreas. In cats, often occurs alongside IBD and liver disease (a combination called "triaditis"). Causes diarrhea, vomiting, decreased appetite, and lethargy.
Exocrine pancreatic insufficiency (EPI) — the pancreas doesn't produce enough digestive enzymes. Causes large volumes of soft, greasy, foul-smelling stool. Rare in cats but treatable.
Other Causes
Stress — moving, new pets, changes in routine, or boarding can trigger stress-related diarrhea that resolves when the stressor is removed.
Medications — antibiotics are a very common cause of diarrhea in cats. Certain medications (NSAIDs, chemotherapy drugs) can also cause GI upset.
Toxins — ingestion of plants (especially lilies), chemicals, or human medications.
What Diarrhea Colors Mean
Brown (normal color, loose consistency) — dietary change, stress, mild infection, or food intolerance. Usually self-limiting.
Yellow or greenish — rapid transit through the intestines (food is moving too fast to be fully digested). Can indicate infection, parasites, or liver/gallbladder issues.
Black or tarry (melena) — digested blood from the upper GI tract (stomach or small intestine). Indicates internal bleeding. Seek veterinary care immediately.
Red blood (hematochezia) — fresh blood from the lower GI tract (colon or rectum). Small amounts may indicate colitis or straining. Large amounts are an emergency.
White or very pale — may indicate liver or pancreatic issues affecting bile production or fat digestion. Uncommon but warrants investigation.
Mucus-covered — thin layer of mucus is normal occasionally. Excessive or persistent mucus suggests colitis or large bowel inflammation.
When Cat Diarrhea Is an Emergency
Seek immediate veterinary care if:
- Bloody diarrhea — especially large amounts of fresh blood or black, tarry stool
- Diarrhea in a kitten — kittens dehydrate extremely quickly and can deteriorate within hours
- Vomiting AND diarrhea together — rapid fluid loss, high risk of dehydration
- Lethargy, weakness, or collapse — the cat can't or won't get up
- Known ingestion of a toxin — lily exposure, medication, chemicals
- No food or water intake for more than 24 hours alongside diarrhea
- Fever — if you can take your cat's temperature (normal is 38–39.2°C / 100.4–102.5°F)
- Diarrhea lasting more than 48 hours with no improvement
- Unvaccinated cat with severe diarrhea — panleukopenia risk
Home Care for Mild Diarrhea
If your cat has mild diarrhea but is otherwise alert, eating, drinking, and active:
1. Don't fast your cat. Unlike dogs, cats should not be fasted when they have diarrhea. Fasting can trigger hepatic lipidosis (fatty liver disease), especially in overweight cats. Continue offering food.
2. Offer a bland diet. Plain boiled chicken (no skin, no seasoning) or a veterinary gastrointestinal diet (e.g., Hill's i/d, Royal Canin GI) for 3–5 days. Avoid rich or fatty foods.
3. Probiotics. Feline-specific probiotics (such as FortiFlora by Purina or Proviable) can help restore healthy gut bacteria. Do not use human probiotics.
4. Ensure adequate hydration. Offer fresh water in multiple locations. Wet food helps maintain hydration. If your cat isn't drinking well, try a water fountain or adding low-sodium chicken broth to water.
5. Monitor the litter box. Track frequency, consistency, color, and any blood or mucus. This information is invaluable for your vet.
6. Maintain litter box hygiene. Clean the litter box more frequently to prevent reinfection (if parasites are the cause) and to reduce stress.
Do NOT give human anti-diarrheal medications (Imodium/loperamide) to cats. Loperamide can cause dangerous nervous system effects in cats.
When to See a Vet for Non-Emergency Diarrhea
Schedule a vet visit if:
- Diarrhea lasts more than 3 days despite bland diet
- It is a recurring pattern — diarrhea that keeps coming back
- Your cat is losing weight
- You've adopted a new cat or kitten — a fecal test should be routine
- The diarrhea is bloody even in small amounts
- Your cat is a senior (10+ years) — chronic disease screening is important
Frequently Asked Questions
Is it normal for kittens to have soft stool?
Mild soft stool can be normal for kittens as their digestive systems mature, especially during weaning or food transitions. However, persistent watery diarrhea, bloody stool, or diarrhea with lethargy is never normal and needs veterinary attention. Parasites are extremely common in kittens.
Can stress alone cause diarrhea in cats?
Yes. Cats are highly sensitive to environmental changes. Moving, boarding, new pets, or even rearranging furniture can trigger stress-related diarrhea. It typically resolves within a few days once the cat adjusts. If it persists beyond a week, other causes should be investigated.
Should I switch my cat's food if it has diarrhea?
If the diarrhea started right after a food change, go back to the previous food and transition more slowly. If your cat has been on the same food and develops diarrhea, a temporary switch to a bland diet (boiled chicken or veterinary GI diet) is appropriate. Long-term food changes should be discussed with your vet.
How can I tell if my cat is dehydrated from diarrhea?
Check for: dry or tacky gums, skin tenting (gently pinch the skin between the shoulder blades — it should snap back immediately; slow return indicates dehydration), sunken eyes, lethargy, and decreased urination. If you suspect dehydration, contact your vet.
Can I give my cat pumpkin for diarrhea?
Plain canned pumpkin (NOT pumpkin pie filling) can help some cats with mild diarrhea due to its fiber content. Start with 1–2 teaspoons mixed into food. However, it's not a substitute for veterinary care if diarrhea is severe or persistent.
My cat has had diarrhea on and off for months. What could it be?
Chronic intermittent diarrhea in cats most commonly points to: food intolerance/allergy, inflammatory bowel disease (IBD), intestinal parasites (especially Giardia or Tritrichomonas), or early intestinal lymphoma. A thorough veterinary workup including fecal testing, blood work, and potentially ultrasound and biopsy is needed to identify the cause.