Why Does My Cat's Poop Smell So Bad? Causes and Fixes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-02

If your cat's poop smells so bad that you can smell it from another room, something in the digestive tract is likely off. Normal cat stool has an odor, but it should not clear a room or make you gag. Diet, parasites, and problems with nutrient absorption are the most common reasons stool turns extremely foul.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• A sudden change in stool odor, especially with diarrhea or soft stool, usually points to diet, a gut infection, or parasites.
• Greasy, pale, bulky stool with a terrible smell can signal malabsorption, including exocrine pancreatic insufficiency (EPI) [1][2].
• Kittens, seniors, and cats with weight loss, vomiting, or blood in the stool need a vet visit sooner.
• Do not change your cat's food abruptly or give human medications without veterinary guidance.
• Bring a fresh stool sample to the appointment if you can, since testing the feces is often the fastest way to find the cause.

What Cat Poop Normally Smells Like

Fresh stool from a healthy cat has a distinct, mildly unpleasant smell. It comes from bacteria fermenting material in the colon and from the breakdown of protein and fat. Once the stool is buried and dries, the odor should fade.

What is normal varies a bit from cat to cat. A cat on a high-protein diet may have slightly stronger-smelling stool than a cat on a moderate-protein food. A cat that just switched foods may have a few days of odd-smelling stool while the gut adjusts.

Signs that the smell is outside the normal range include:

• Odor that lingers in the room after the box is scooped
• A sour, rotten, or metallic smell
• Stool that is greasy, shiny, or pale
• Stool that is unusually large or soft
• Odor paired with gas, vomiting, weight loss, or appetite changes

If your cat also has bad breath, that can point to a separate problem in the mouth. You can read more about that in Why Does My Cat's Breath Smell?.

Why Cat Poop Smells So Bad: Main Causes

Several conditions can make stool smell far worse than usual. Some are minor and easy to fix. Others need treatment.

Diet and Food Intolerance

Food is the most common and most fixable cause of smelly stool. A sudden switch to a new brand, a new protein, or table scraps can throw off the gut bacteria that ferment waste. The result is looser, smellier stool and more gas.

Some cats have a true intolerance to a specific ingredient. The stool tends to be soft and foul for weeks, not days. Your cat may also scratch, vomit, or lose weight. If your cat has gas along with the odor, see Why Does My Cat Have Gas?.

Parasites and Infections

Intestinal worms, giardia, coccidia, and other parasites damage the gut lining and change how food is digested. That produces stool that smells sharply different from normal. Diarrhea that smells really bad is a common clue, especially in kittens or cats from shelters.

Bacterial and viral infections can cause sudden, watery, foul diarrhea. These often come with vomiting, lethargy, or fever. A cat that stops eating or drinking needs care right away.

Malabsorption and Exocrine Pancreatic Insufficiency

When the pancreas does not make enough digestive enzymes, food is not broken down or absorbed properly. This is called exocrine pancreatic insufficiency, or EPI [1][2]. The stool becomes loose, voluminous, and greasy, and it smells terrible [1]. Cats with EPI often lose weight even though they eat well, and they may have oily fur around the rear end [1][3].

EPI is diagnosed with a blood test called feline trypsin-like immunoreactivity [1][2]. Treatment involves enzyme supplementation, diet changes, and often cobalamin (vitamin B12) supplementation [1][2]. Most cats respond well and can live a normal life [1].

Chronic Diarrhea and Gut Disease

Chronic diarrhea in cats has many causes, including osmotic and secretory diarrhea, a leaky gut barrier, and abnormal gut motility [4]. Long-term inflammation in the intestines can change the stool's smell and consistency. These cases need a full workup, and nutrition is a core part of long-term management [4].

Anorectal Problems

Growths called rectal polyps can form in the rectum. They are usually benign and do not spread [5]. Signs include straining to defecate, blood in the stool, and diarrhea [5]. A vet can often feel a polyp during a rectal exam, and its surface tends to bleed easily [5]. Surgery usually leads to a quick recovery [5].

Red Flags: When Smelly Poop Is an Emergency

Some signs mean you should call your vet or an emergency clinic right away.

• Your cat is vomiting and cannot keep water down.
• There is a lot of blood in the stool, or the stool looks black and tarry.
• Your cat is weak, wobbly, or unresponsive.
• The belly looks swollen or feels painful when touched.
• Your cat has not eaten for more than 24 hours.
• A kitten or senior cat has watery diarrhea for more than a few hours.

If you think your cat ate something toxic, call the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. These lines may charge a consultation fee.

What You Can Do at Home While You Wait

You cannot fix every cause of smelly stool at home, but a few safe steps can help while you wait for your appointment.

• Keep the litter box clean. Scoop at least once a day so you can track changes in color, shape, and odor.
• Do not switch foods abruptly. If you change diets, do it slowly over 7 to 10 days by mixing small amounts of the new food into the old.
• Stop all table scraps and treats for a few days. Treats are a common hidden cause of gut upset.
• Make sure fresh water is always available. Diarrhea can lead to dehydration.
• Collect a fresh stool sample in a clean bag or container. Bring it to the visit if it is less than 12 hours old.
• Do not give human anti-diarrhea medicines, antibiotics, or dewormers without asking your vet first. Some are toxic to cats.

If your cat is also missing the litter box, that can be a separate issue. See Why Is My Cat Pooping Outside the Litter Box? Causes and Solutions.

What Your Veterinarian Will Check

Your vet will start with a full history. Be ready to describe when the odor started, what the stool looks like, how often your cat goes, and whether anything changed in the diet or routine.

The physical exam includes:

• Weight and body condition
• Abdominal palpation to check for pain, masses, or thickened bowel
• A rectal exam to look for polyps or other problems [5]
• Hydration status and gum color

Common tests include:

• Fecal flotation and fecal antigen tests for parasites
• Fecal culture or PCR for infections
• Blood work, including a complete blood count and chemistry panel
• Feline trypsin-like immunoreactivity to check for EPI [1][2]
• Cobalamin (vitamin B12) level, which is often low in EPI [1]
• Imaging such as X-rays or ultrasound if the vet suspects a mass or chronic disease

If the stool is chronic and the cause is unclear, your vet may recommend an endoscopic exam or a diet trial [4]. Rectal polyps may need endoscopy to see clearly, and a tissue sample may be sent to a lab to confirm the diagnosis [5].

Prevention and Monitoring

You can lower the chance of smelly stool and catch problems early with a few habits.

• Feed a consistent, high-quality diet. If your cat does well on a food, avoid frequent changes.
• Introduce any new food slowly over 7 to 10 days.
• Keep up with parasite prevention as your vet recommends.
• Schedule routine wellness visits, especially for kittens and senior cats.
• Track your cat's litter box habits. Note the color, shape, and smell of stool.
• Watch for weight loss. Weigh your cat monthly if you can.
• Treat other health problems early. Dental disease, ear infections, and skin issues can all affect overall health. For example, see Cat Ear Infection with Odor: Causes and Treatment and Why Is My Cat So Itchy?.

If your cat has EPI, long-term monitoring matters. Most cats need lifelong enzyme replacement and cobalamin supplementation, and some need diet changes [1][2]. Regular checkups help your vet adjust the plan.

Limitations and When to Contact a Veterinarian

This article gives general information, not a diagnosis. Every cat is different, and only a veterinarian who examines your cat can determine the cause and the right treatment.

Contact your vet the same day if:

• Diarrhea lasts more than 24 hours in an adult cat or more than a few hours in a kitten
• Your cat is eating less or losing weight
• You see blood or mucus in the stool
• The odor changed suddenly and does not improve in 2 to 3 days
• Your cat seems uncomfortable or is straining to poop

Go to an emergency clinic now if:

• Your cat is vomiting repeatedly or cannot keep water down
• Your cat is weak, collapsed, or having trouble breathing
• The stool is black and tarry or contains a large amount of blood
• Your cat's belly is swollen and painful
• You suspect your cat ate something toxic

For routine concerns, schedule a visit within a few days. Bring a fresh stool sample and a list of everything your cat eats, including treats and supplements.

Frequently Asked Questions

Why does my cat's poop smell worse than my other cat's?

Diet, gut bacteria, and overall health differ from cat to cat, so stool odor varies. If one cat's stool is much worse and the cat also has soft stool, weight loss, or gas, a vet visit is a good idea. Testing can rule out parasites, EPI, and other causes.

Can I change my cat's food to fix the smell?

Sometimes a diet change helps, but only if food is the cause. Switch foods slowly over 7 to 10 days to avoid making diarrhea worse. Ask your vet which diet fits your cat's age and health needs before you switch.

Is smelly poop ever normal after a diet change?

Yes. A short period of softer, stronger-smelling stool can happen when you change foods. It should improve within a week or two. If it lasts longer or comes with vomiting or weight loss, call your vet.

Does smelly poop mean my cat has worms?

Not always, but parasites are a common cause. Worms and other parasites can change stool odor and cause diarrhea. A fecal test at your vet's office is the only way to know for sure.

Can stress make my cat's poop smell bad?

Stress can affect digestion and lead to softer stool, which may smell stronger. Changes like a new pet, a move, or a new litter can trigger this. If the problem lasts more than a few days, have your vet check for medical causes first.

Related Articles

• Why Does My Cat's Breath Smell?
• Why Is My Cat Pooping Outside the Litter Box? Causes and Solutions
• Cat Ear Infection with Odor: Causes and Treatment
• Why Is My Cat So Itchy?
• Why Does My Cat Have Gas?
• Cat Straining to Poop but Only Passing Mucus: Causes and Care

References

1. Exocrine pancreatic insufficiency in the cat. Topics in companion animal medicine, 2012.
2. Exocrine pancreatic insufficiency in dogs and cats. Journal of the American Veterinary Medical Association, 2024.
3. Gastrointestinal microbiota and fecal fatty acids of cats with exocrine pancreatic insufficiency. Journal of feline medicine and surgery, 2026.
4. Feline chronic diarrhea: causes and nutritional management. Veterinary and animal science, 2026.
5. Disorders of the Rectum and Anus in Cats - Cat Owners. Merck Veterinary Manual.

Further Reading

• Merck Veterinary Manual: Cat Owners
• Cornell Feline Health Center: Health Information
• American Veterinary Medical Association: Pet Care