Why Does My Cat’s Poop Smell So Bad?

Last Updated on October 23, 2021 by Julia Wilson

What is a normal cat stool like?

Normal cat feces does have a particularly strong odour. Researchers found that cat feces contains a malodorous material known as MMB with the chemical structure 3-mercapto-3-methyl-1-butanol. This derivative of feline, a sulphur-containing amino acid present in cat urine is thought to play a role in marking.

There will be an odour to the stool, but it should not be so overpowering, that you can smell it in the next room.

Keeping an eye on your cat’s stools is important as they can sometimes reveal an underlying health condition.

  • Cats usually defecate (pass a stool) between one to two times a day
  • The stool should be well-formed, and soft, not watery or in dry and/or in pellets
  • The normal colour for a stool is chocolate brown

Causes of smelly feces

Low-quality food

All commercial dry cat food contains some form of carbohydrate fillers which are necessary for the pellets to hold their shape. Cheap brands of cat food can contain higher levels of low-quality fillers to produce cost-effective food.

Fillers (such as corn and other grain fillers) are not a part of the cat’s natural diet and are poorly digested, which can often lead to GI upset, along with flatulence and smelly feces. Corn is

It is also worth noting that cheap products don’t necessarily save money because they are lower in nutritional value than premium brands; the cat needs to consume more to meet its dietary needs.

By law, cat food packaging must label its ingredients in order of the highest level to the lowest level, so always look for brands which list meat/s (such as chicken, beef, lamb) in first, and preferably second and third too.

Some cats do just fine on cheap cat food; in my experience, cheap brands did cause their feces to take on a much stronger smell. They have since been switched to a mid-range brand (along with raw chicken wings), and there is a noticeable improvement in their feces. All pet foods (even cheap brands) which have the words ‘complete and balanced‘ on their packaging must meet AAFCO standards.

Bacterial infection

Salmonella and Escherichia coli are bacteria that can live in the gastrointestinal tract of cats, causing inflammation and strong-smelling feces. The most common route of infection is via contaminated food or water and hunting (especially birds).

A sudden change in diet

Some cats can be sensitive to changes in diet which can lead to mild stomach upset. Even if you haven’t changed brands, the pet food manufacturer may have changed an ingredient that can cause an upset.

If you do want to swap the type or brand of food you feed your cat, do so gradually, over several days by adding a small amount of the new food to the current food, increasing the new food while decreasing the old food.

Food intolerance

Food intolerance is an adverse reaction to food, one of its ingredients or additives. It differs from a food allergy in that there is no immune system involvement. Food allergies typically cause nonseasonal itching, especially around the head and face, swollen and inflamed areas on the face and ears, hair loss due to itching, vomiting, strong-smelling feces, and diarrhea.

A common food intolerance that many people have heard of is milk. This is because mammals stop the production of lactase, the enzyme necessary to digest lactose, which is the major sugar in milk.

Other causes of food allergies and intolerances in cats are fish, beef, eggs, wheat, and milk. Cats can become allergic and intolerant to foods they have eaten for a long period.

Maldigestion and malabsorption

Maldigestion and malabsorption are several disorders in which the small intestine can’t absorb enough of single or multiple nutrients. There are many steps involved in the process of digestion, and any defect can cause malabsorption.

Litter tray issues

Most cats are hardwired to bury their feces to avoid alerting predators to their presence. If you have a cat who is not burying his or her feces, there may be an issue with the litter tray. Possible causes include dirty litter trays, inter-cat bullying, the type of cat litter or litter tray and the location. Cats feel vulnerable when they are defecating, and if a cat is being harassed by another cat, he or she may deposit their feces, and then scoot from the area.

Dirty litter trays can be offputting to cats. Solids should be removed at least twice a day, and trays emptied, cleaned and refilled with fresh litter once a week. There should be one tray per cat, plus one extra. Instead of lining them up next to each other, place them in different locations.

What should you do?

Any changes to your cat’s stool, including an abnormally strong odour should be evaluated by a veterinarian if it does not return to normal within 24-48 hours. Bring along a stool sample which may provide a pointer as to the underlying cause.

In the meantime, switch the cat to a bland diet of boiled chicken and rice. This will help to rest the gastrointestinal tract and can help relieve the issue of smelly feces.

It can be hard to identify whose feces belongs to which cat in multi-cat homes. If you suspect one cat is producing smelly feces, feed each cat separately and shave a small amount of non-toxic Crayola shavings to the food. Each cat has his or her unique colour, make a note so you don’t forget. The shavings will safely pass out of the the cat via the feces, which can help to identify the cat with the smelly stool.


The veterinarian will obtain a medical history from you, which may include:

  • How long have the feces been smelly?
  • What is the consistency of the feces?
  • What do the feces look like? Dry, pale, frothy, greasy, bloody?
  • What is the cat eating and drinking?
  • Is the cat on any medications or supplements?
  • Do you treat the cat for parasites?
  • Are there any accompanying signs?
  • Do the symptoms come and go?

Diagnostic workup:

Baseline tests: Complete blood count, biochemical profile and urinalysis to evaluate the overall health of the cat

Fecal flotation: A small sample of stool is mixed in a tube with a liquid flotation solution, the solution is strained to remove solids and centrifuged for five minutes. A coverslip is placed over the tube and left for ten minutes. The coverslip is removed and placed liquid side down on a microscope slide and evaluated for worm eggs.

Fecal smear: A thin smear of feces is examined under a microscope to identify Giardia trophozoites.

Snap test: IDEXX Laboratories have a SNAP Giardia test kit which is available for in-house testing, the sensitivity of this test is 90%.

Diagnostic imaging: Radiographs or ultrasound to evaluate the organs, look for cancer.


This will depend on the underlying cause but may include:

  • Gradually change the cat over to a high-quality diet, this should occur over a period of 4-5 days by slowly introducing more of the new food and reducing the previous food.
  • Avoid milk or other food products which may be the cause of food intolerances.
  • Regularly treat your cat for intestinal worms.
  • Address the underlying cause of cats with pancreatitis as well as supportive care including pain relief, anti-nausea medication, fluids as well as nutritional support.
  • Lifelong administration of pancreatic enzyme extract, high protein low fibre diet and vitamin B12 for cats with pancreatic enzyme insufficiency.
  • Dietary modifications, corticosteroids or other drugs to suppress the immune system and in some cases, antibiotics to treat inflammatory bowel disease.