A veterinarian explains how psyllium fiber supports stool consistency in cats, why that matters for anal gland impaction, and what the evidence shows.
By Dr. Dody Tyneway Robi, DVM | Updated November 2026
Psyllium is a fiber that holds water, softening stool that is too hard and giving form to stool that is too loose. In a six-month controlled trial of 49 cats with chronic constipation, cats fed a diet with 6% psyllium kept softer stools and were far less likely to fail on the diet than cats fed a similar diet with 0.5% psyllium (1). That matters beyond constipation, because stool quality is also what keeps a cat's anal glands emptying the way they should.
Lexi, age 12: a small change in the litter box
Lexi's problem started with something small. Her owner noticed she seemed uncomfortable when picked up, and for about a week she kept licking under her tail. Her bowel movements had also become a bit firmer and less regular. Most cats have a bowel movement daily or every other day. What matters is a change in that pattern, which was the case for Lexi.
The cause turned out to be an impacted anal gland, which surprised her owner. By the time Lexi was seen, the impaction had progressed to an abscess that ruptured through the skin beside her anus. That is the consequence when a gland cannot empty as it should: the trapped material thickens, bacteria multiply in it, the sac swells and becomes infected, and eventually the abscess breaks open to drain. Anal gland problems are uncommon in cats, which is part of why they get missed. Cats hide discomfort well, and licking can look like normal grooming. Discomfort when lifted, licking or biting at the hind end, scooting, a strong fishy smell, straining in the litter box, and swelling or redness beside the anus are all reasons to call your veterinarian.
The photo below shows Lexi's ruptured anal gland abscess after the area was shaved for treatment.
How common are anal gland problems in dogs and cats?
Dogs are affected far more often than cats. In a survey of general-practice veterinarians in the Netherlands, respondents estimated that anal sac disease affected about 15.7% of the dogs they saw and about 0.38% of the cats (2). Impaction was the most common form in both species, at roughly 8.9% of dogs and 0.25% of cats. These figures are veterinarians' estimates rather than counts from medical records, so they are approximate. The pattern agrees with earlier canine studies, which put the figure between 4.9% and 12.5% depending on the population (2).
About a third of responding veterinarians thought anal sac disease was more common in obese animals, while most saw no difference, and the authors note that earlier studies have tied a higher body condition score to anal sac problems (2). In my experience, it is more common in overweight cats. Many are also arthritic, which makes it harder to crouch and generate the abdominal press that normally helps empty the glands.
How are a cat's anal glands supposed to empty?
The two anal sacs sit just inside the anus at roughly the four and eight o'clock positions. Picture each one as a small tube of toothpaste, cap pointing toward the opening. When a firm, well-formed stool moves through the rectum, it presses on both tubes, and a little scent material comes out with every bowel movement.
Stool that is too soft slides past without pressing the tubes. The material stays in, thickens, and becomes harder to empty. Diarrhea also irritates the skin around the anus, and irritated tissue swells around the openings of the ducts.
Stool that is too hard creates a different problem with the same result. Passing it hurts, so a cat may hold it, then strain. Hard stool and repeated straining inflame the tissue around the anus, and inflammation narrows the ducts. The tube gets squeezed, but the cap is swollen shut.
Both ends of the stool problem lead to the same place.
Body weight adds a third pressure. Fat around the hind end cushions the tubes from the squeeze, and the survey authors note that perianal fat can compress the ducts and hold material in (2). In my practice, I also see the grooming side of this: an overweight cat often cannot reach that area to clean it, so residue and moisture stay on the skin and the irritation never quite settles.
What does psyllium do in a cat's colon?
Psyllium husk is mostly soluble fiber. It holds water in the colon, so hard stool stays softer and passes with less effort. It adds bulk, which gives the colon something to move. With loose stool, the same gel takes up free water and helps the stool hold its shape. In people, psyllium's role as a stool normalizer for both constipation and diarrhea is well established (3).
The feline evidence is narrower but solid where it exists. In the 2026 trial, client-owned cats with recurring constipation were randomly assigned to a dry gastrointestinal diet containing 6% psyllium or a similar diet with 0.5% psyllium, and the trial was blinded (1). Over six months, 26.9% of cats on the psyllium-rich diet failed on it (constipation did not improve, new digestive signs appeared, or the cat had to switch diets), compared with 73.3% on the control diet. Stool consistency improved more on the psyllium diet at nearly every recheck. If you are managing constipation now, my post on what food is best for cats with constipation covers moisture, diet changes, and when to see your veterinarian.
The trial tested a single dry extruded therapeutic diet, and Royal Canin scientists were among the authors, so the results describe psyllium in that particular food. The trial enrolled only cats with constipation. It did not measure anal gland problems at all, and it did not test psyllium for loose stool in cats.
A high-fiber diet is commonly recommended in the veterinary literature for preventing anal sac disease (2), but no controlled study has tested psyllium for preventing anal gland impaction in cats. Using it for that purpose rests on mechanism and clinical experience, not trial data.
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How can stool quality help prevent another impaction?
For Lexi, the goal is a formed, comfortable stool every day, so the glands empty as they should. She does not have obvious signs of arthritis, but in cats the signs are often subtle and overlooked. When researchers reviewed radiographs from 100 cats older than twelve, about 90% showed degenerative joint disease somewhere in the skeleton (4). Those were cats being imaged for other reasons, and changes on an X-ray do not always mean pain, but at Lexi's age it is reasonable to assume some joint change is present. A stiff cat has a harder time crouching to pass stool and turning to groom.
Stool consistency comes first, which is where psyllium fits: introduce it in small amounts and increase slowly while watching the litter box. Hydration comes with it, because fiber without enough water can make hard stool worse; moist food helps here. If she is carrying extra weight, gradual weight loss helps on two fronts, reducing fat around the hind end and letting her groom again. Weight loss in cats has to be slow and supervised, because rapid loss can trigger hepatic lipidosis, a serious liver condition. Finally, any underlying cause of soft stool or itchy skin, such as a food reaction, deserves its own workup, since chronic soft stool and skin inflammation are among the risk factors veterinarians most often report (2).
No one can promise Lexi will never have another impaction. With steadier stool, a healthy weight, and an owner who now knows what the licking meant, her odds are good.
Psyllium is not right for every cat. Cats with severe constipation or megacolon, obstipation, a suspected intestinal blockage, or dehydration need a veterinarian's plan before adding any fiber, and cats with kidney disease need extra attention to water intake. Use plain, unflavored psyllium only. Many human fiber products contain sweeteners and flavorings that don't belong in a cat's bowl.
Frequently asked questions
Can I give my cat psyllium husk?
Many cats tolerate psyllium well, and a controlled trial supports its use for chronic constipation (1). Check with your veterinarian first, especially if your cat is constipated now, is dehydrated, or has kidney disease or megacolon. Use plain psyllium with no added sweeteners or flavors.
How much psyllium should a cat have?
Check with your veterinarian first. In my experience, adding a pinch to ¼ teaspoon of plain psyllium husk to moist food twice daily is generally safe for a healthy adult cat. Start at the low end, make sure your cat is drinking well, and watch the litter box as you adjust. If your cat is not having a normal stool every day or two, talk with your veterinarian before adding fiber.
Who should not have psyllium husk?
Cats that are vomiting, dehydrated, in pain, or not eating should not be given psyllium. Neither should cats with severe constipation, megacolon, or a suspected blockage. Psyllium needs water to work, so a cat that is not drinking well can end up with harder stool. Cats with kidney disease need their veterinarian's input first, and because fiber can slow the absorption of some medications, check with your veterinarian if your cat takes any.
What are the signs of anal gland problems in cats?
Licking or biting under the tail, discomfort when picked up, scooting, a strong fishy odor, straining to pass stool, and redness or swelling beside the anus. A swelling that opens and drains may be an abscess and needs prompt veterinary care.
Do overweight cats get anal gland problems more often?
The evidence is mixed. Some studies tie a higher body condition score to anal sac disease, and fat around the hind end can compress the ducts (2). In a veterinary survey, about a third of respondents thought obese animals were affected more often, while most saw no difference. In my practice, overweight cats that cannot groom themselves seem more prone to irritation in that area.
Why do dogs get anal gland problems more than cats?
Veterinarians estimate anal sac disease in about 15.7% of dogs seen in general practice, compared with about 0.38% of cats (2). The reasons are not fully understood. According to surveyed veterinarians, small breed dogs, dogs with skin allergies, and dogs with chronic loose stool appear to be at higher risk (2).
Does my cat need its anal glands expressed regularly?
Most cats never do. In my experience, routine expression of healthy glands can irritate the tissue. Expression treats a problem; a cat that needs it repeatedly has an underlying cause worth finding.
References
- Rochon J, Charles H, Biourge V, Laxalde J, Goñi García-Falces M, Dito D. A psyllium-supplemented gastrointestinal diet is effective for the management of chronic constipation in cats: a 6-month controlled clinical trial. Journal of Feline Medicine and Surgery. 2026. doi:10.1177/1098612X261420519
- Corbee RJ, Woldring HH, van den Eijnde LM, Wouters EGH. A cross-sectional study on canine and feline anal sac disease. Animals. 2022;12(1):95. doi:10.3390/ani12010095
- McRorie JW Jr, McKeown NM. Understanding the physics of functional fibers in the gastrointestinal tract: an evidence-based approach to resolving enduring misconceptions about insoluble and soluble fiber. Journal of the Academy of Nutrition and Dietetics. 2017;117(2):251-264. doi:10.1016/j.jand.2016.09.021
- Hardie EM, Roe SC, Martin FR. Radiographic evidence of degenerative joint disease in geriatric cats: 100 cases (1994-1997). Journal of the American Veterinary Medical Association. 2002;220(5):628-632. doi:10.2460/javma.2002.220.628
This article is for educational purposes and is not a substitute for veterinary care. If your cat shows signs of anal gland discomfort or changes in stool, please see your veterinarian.
