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Most cats experience a brief episode of diarrhea from time to time, and the cause is often something benign, like a too-sudden change from one brand of food to another. But the possible causes of diarrhea also include dangerous, even fatal, health issues, so it’s important to know what clues to look for. Ongoing diarrhea may indicate an underlying chronic illness. How do you know what’s causing your cat’s diarrhea? When should you see your veterinarian? And how can you help your cat feel better? 


Diarrhea—meaning stool that’s softer and wetter than normal—actually includes a range of consistencies, from moist shapes to watery liquid. When it begins suddenly and lasts for less than two weeks, diarrhea is described as acute. Diarrhea is considered chronic if it continues or recurs over a period of three weeks or more.


A healthy, “normal” cat poop is generally dark brown, firm (but not hard), and shaped like logs or nuggets. Moist logs or even a wet “flop” from time to time probably isn’t cause for alarm. But if your cat has very soft or liquid bowel movements for more than a day or two, it’s important to identify the underlying cause, since diarrhea can sometimes indicate serious, even potentially fatal, health situations. 


Is your cat producing soggy logs, soft piles, or puddles? To determine where your cat’s poop falls on the scale, check out our Fecal Scoring Chart.

Cat Fecal Scoring Chart - Cat Poop Chart

Why Does Your Cat Have Diarrhea?

Diarrhea is one of the top reasons cats are seen by veterinarians. Digestive upset can be triggered by a wide range of factors, so figuring out the true cause of your cat’s diarrhea may be tricky. Here are some of the most common causes of diarrhea in cats.

Diet

Cats are obligate carnivores, meaning that they can’t get all the nutrients they need from plant sources. So cats do best on a diet that’s high in protein and very low in carbohydrates. But many commercial cat foods contain high levels of carbohydrates, which can encourage the growth of certain types of gut bacteria, such as Prevotella, that thrive in low-protein, high-carbohydrate environments. When these bacteria become too abundant, they can create unhealthy levels of inflammation, leading to diarrhea and even inflammatory bowel disease (IBD).


An abrupt change in your cat’s diet can trigger diarrhea. Even if your cat doesn’t usually have a “sensitive stomach,” any new food can upset the digestive system at first. To avoid digestive symptoms when you switch your cat from one brand or variety to another, it’s best to transition gradually from the old food to the new food over 7–10 days.


Food intolerance, also called food hypersensitivity—the body’s inability to digest a particular food properly—is another frequent cause of diarrhea. A newly introduced food may cause diarrhea if your cat can’t digest one or more of its ingredients. In other cases, cats may develop a hypersensitivity to a protein source they’ve eaten for years with no problem. The solution usually involves identifying and eliminating the offending ingredient in the cat’s diet—for example, by transitioning to a “novel” protein source that the cat has never been fed before.


Human food 

You may sometimes be tempted to treat your cat with bits of your own food, but that’s generally not a good idea. With a very few exceptions, human foods aren’t good for cats, and some are actually toxic. Foods that are poisonous to cats include chocolate, avocado, grapes/raisins, onions, garlic, alcohol, and the sweetener Xylitol (found in some chewing gums).


Dairy products are also problematic because, while many adult cats love milk, they lack the enzyme that’s required to break down lactose, the sugar found in milk. The inability to digest lactose, known as lactose intolerance, is a well-known cause of diarrhea in cats. 


Toxins

Ingestion of toxic (poisonous) substances can cause diarrhea, as well as other symptoms, such as vomiting, drooling, seizures, sluggishness, and an unsteady gait. Numerous substances found around the house—such as insecticides, rodenticides, cleaning agents, and antifreeze—will sicken or kill a cat if ingested. 


Eating any plant may cause diarrhea or vomiting, but many common indoor and outdoor plants—lilies, tulips, poinsettias, foxglove, and philodendron, among many others—are toxic to cats and may cause fatal illness if even a small piece is eaten.


Human medications are another common cause of feline poisoning.


If you think your cat might have eaten something toxic, call your veterinarian or the ASPCA Animal Poison Control Center (888-426-4435) immediately.

Foreign objects

Many cats enjoy chewing on things that aren’t food, such as cardboard or toys, but if such items are swallowed, they can irritate the digestive tract or even end up lodged in the intestine, creating a dangerous obstruction. A blockage can cause diarrhea because, while the obstruction prevents solid feces from moving through the intestines, liquid may seep around it. 


String, yarn, ribbons, elastics, and the like are especially hazardous because of the tiny barbs on a cat’s tongue, which point toward the throat to pull food in. Once a piece of yarn or fabric gets caught on those barbs, it’s very difficult for your cat to avoid swallowing it. And if one end gets caught and anchored in the mouth, the length that extends into the digestive system can cause severe internal injuries. Playing with string is great exercise for your cat, but it’s important to supervise whenever anything string-like is around.


Parasites

Parasites are eukaryotic organisms that infect hosts and cause them harm. Some of the parasites that infect cats are large, multicellular organisms, including flatworms (flukes and tapeworms), roundworms (Toxascaris and Toxocara), and hookworms (Ancylostoma and Uncinaria). Other parasites are single-celled protozoa, such as Giardia, Tritrichomonas, and coccidia (Cystoisospora, Cryptosporidium, and Toxoplasma). Any of these parasites can irritate the gastrointestinal tract and cause diarrhea, as well as other symptoms, such as vomiting, a dull coat, and dehydration. 

 

Stress

Many cats are extremely sensitive to changes in their environment or routine. Fireworks, a trip in the car, or a new person or animal in the house, for example, can be very stressful for some cats. In cats and humans alike, the body reacts to stress by releasing hormones and other chemicals that disrupt the gut microbiome, often resulting in short-term diarrhea.


Medications

Many prescribed veterinary medications may cause diarrhea as a side effect, including steroids, non-steroidal anti-inflammatory drugs (NSAIDs), heart medications, bronchodilators (for asthma), and anti-anxiety drugs. But the most common diarrhea-causing medications are antibiotics, which disrupt the gut microbiome by killing off a lot of beneficial bacteria along with the pathogens they’re meant to target. Metronidazole (Flagyl) is an antibiotic and antiprotozoal medication that’s frequently prescribed for cats—for example, to treat periodontal disease, bacterial infection, and even unexplained diarrhea. But this particular drug has been found to cause long-term damage to the gut microbiome and is less effective for many GI conditions than previously thought.


Illnesses

A number of diseases and health conditions can cause chronic diarrhea in cats. These include infections caused by certain bacteria:

  • Salmonella
  • Campylobacter
  • Clostridium perfringens

And viral infections:

Other conditions that commonly cause diarrhea include:


Gut microbiome imbalance

Diarrhea is often a sign that the gut microbiome is out of balance, meaning that some of the beneficial gut bacteria necessary for healthy digestive and immune functions are missing or aren’t present in the right proportions. Such imbalances may result from a variety of causes. A diet that’s too high in carbohydrates can cause certain bacteria groups, like Firmicutes, to grow so numerous that they crowd out other important groups. A course of antibiotics can kill off a lot of beneficial gut bacteria in addition to the harmful bacteria it’s meant to treat. Certain chronic illnesses, including some cancers, continually disrupt the bacterial populations in the gut, leading to ongoing imbalances.



Your Cat’s Digestive System

As obligate carnivores, cats don’t need the longer gastrointestinal (GI) tracts required by omnivores like dogs and humans, who eat a much broader diet, or herbivores like cows and rabbits, who eat plants. A cat’s digestive tract is relatively short, and a high-protein meal moves through quickly. It typically takes a cat’s food about 20 hours to pass through the whole GI tract, whereas in a human, digestion may take as long as 72 hours. The fast transit rate of food through the feline GI tract reflects its adaptation to a hunting lifestyle, making the cat ready to pounce on the next prey item.

Cat Digestive System: A cat’s digestive tract is relatively short, and a high-protein meal moves through quickly.

Different illnesses arise in different parts of the intestinal tract, so in figuring out the cause of your cat’s problem, it’s helpful to determine whether the diarrhea originates in the small intestine or the large intestine (colon).

For example, because the small intestine is where most nutrients get absorbed, problems here can mean the body is missing out on a lot of the nutrition in your cat’s food, which can create additional problems, like weight loss and nutrient deficiencies. Your cat’s poop can offer important clues:

How to Tell if Your Cat's Diarrhea Is Coming From the Small Intestine or the Large Intestine


The color of your cat’s poop may also help you figure out what’s going on. This chart describes the most common poop colors and what causes them:

Cat Fecal Color Chart: Cat Poop Color

A Note on Kittens

Diarrhea is even more common in kittens than in adult cats. A kitten’s digestive system is still adjusting to solid food, and even small dietary changes are likely to cause intestinal upset. Kittens are more vulnerable to intestinal parasites and pathogens because their immune systems are still developing. They are also more likely to ingest things that might be toxic or could create intestinal blockages. And certain diseases that cause diarrhea are more common in kittens, such as feline enteric coronavirus (FeCV) and FIP.


Because kittens are small, diarrhea can quickly lead to severe dehydration and weakness. So if your kitten has diarrhea that lasts for more than two days or that is accompanied by other symptoms, contact your veterinarian right away.


When to See a Veterinarian

In an adult cat, a loose stool from time to time isn’t cause for concern. And if your cat is otherwise behaving normally and seems to feel fine, it’s reasonable to wait a day or two to see if the diarrhea will resolve on its own.


But if your cat’s diarrhea lasts longer than two days or is accompanied by additional clinical signs—such as vomiting, poor appetite, or lethargy—it could indicate a serious health issue. And if you think your cat might have ingested something poisonous or swallowed a foreign object, you should see your veterinarian immediately.


Your veterinarian may use a number of diagnostic approaches in investigating the cause of your cat’s diarrhea, including a physical exam, fecal parasite test, blood work, urinalysis, and imaging (such as x-ray or ultrasound).



Tips for Stopping Your Cat’s Diarrhea

Whether the cause of your cat’s diarrhea has been identified or is still under investigation, there may be several ways you can help your cat feel better. Here are some tips:


Avoid medications. Never give your cat any human anti-diarrheal medication, since many of these are toxic or fatal to cats. Avoid antibiotics unless they’re absolutely necessary, since most antibiotics can worsen or cause diarrhea. If your cat has a bacterial infection and your veterinarian determines that antibiotics are necessary, you can support your cat’s gut health during and after the course of medication.

Feed the right diet. Check with your veterinarian before making any changes to your cat’s diet. If your cat’s usual food is high in carbohydrates, ask about gradually adding more protein. Make sure you’re feeding a high-quality, cat-appropriate diet. It’s probably best to eliminate treats and any other extras until the diarrhea has been resolved. And always provide your cat with plenty of fresh water. 


Don’t withhold food. Fasting your cat for a few hours is often recommended for vomiting, but it’s unlikely to help diarrhea. (Never withhold food from a cat for any reason for more than 24 hours; insufficient nutrition over just a few days can lead to a potentially fatal liver condition in cats.)


Add fiber and prebiotics. Adding certain sources of fiber to your cat’s food—particularly the prebiotic fibers inulin and psyllium—can improve diarrhea both by absorbing excess water in the intestines and by providing food for beneficial bacteria that live in the intestinal tract. Always start with a very small amount of any fiber.


Especially if your cat’s diarrhea is a result of a course of antibiotics, AnimalBiome’s Gut Maintenance Plus (for both cats and dogs) can help. Containing the probiotic yeast S. boulardii, the prebiotic MOS, and a bacteriophage cocktail called PreforPro, our Gut Maintenance Plus product was specifically designed to resolve diarrhea caused by antibiotics.


Test your cat’s gut health. Microbiome testing can tell you a lot about what’s going on in your cat’s digestive system and even how to correct certain problems. By identifying all the different kinds of bacteria in your cat’s gut, a Gut Health Test can determine whether those bacterial populations are present in balanced amounts when compared to the gut microbiomes of healthy cats.

 

Like humans, cats depend on the bacteria that live in the GI tract to help digest their food and extract its nutrients. A diverse, well-balanced gut microbiome also supports the immune system, keeps your cat’s coat healthy, and even promotes a happy mood. But when some beneficial bacteria populations are missing, the microbiome becomes imbalanced, and important digestive and immune functions may no longer work properly.

 

Dietary changes may be enough to adjust the balance among your cat’s resident gut bacteria groups. Transitioning to a higher-protein, lower-carbohydrate diet, for example, may improve your cat’s gut health by encouraging the growth of the important Fusobacteria group, which thrives in a high-protein environment.

 

For cats with chronic diarrhea caused by more serious microbiome imbalances or IBD, Gut Restore Supplements can help bring balance to the gut and relieve symptoms. Offering the benefits of fecal transplant in a capsule, Gut Restore Supplements supply missing beneficial bacteria and help crowd out harmful ones by providing an entire community of healthy cat-specific gut microbes.

A Note on Shelter Cats

In animal shelters, cats with diarrhea typically aren’t adopted out as quickly as healthy animals and are therefore more vulnerable to euthanasia. Read Marigold’s story: this shelter cat with chronic diarrhea found a forever home and a solution to her digestive problems.

 Because chronic diarrhea is such a serious problem for cats at animal rescues and shelters, we help support these organizations by offering product discounts and by periodically donating microbiome tests and supplements.


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