Dog anal glands, more correctly called anal sacs, are two small pouches just inside the anus that hold a strong-smelling fluid. They normally empty a little each time a dog poops.1,2 When they don't empty properly they can become impacted, infected or abscessed. Anal sac problems are the most common disease of a dog's anal region, diagnosed in about 1 in 23 dogs each year in UK veterinary practices.3,4 This guide covers what the glands do, the signs of trouble, which dogs are prone, whether you should express them at home, anal sac cancer, treatment and prevention.
See a vet the same day if your dog has:
- A red, hot or painful swelling beside the anus, or a burst sore draining blood or pus (possible abscess)2,3
- Painful straining to poop, or cries when sitting or when the tail is touched3,2
- A firm lump near the anus, especially in an older dog, or sudden heavy thirst and urination along with straining (possible anal sac tumor)5,2
What the Research Shows
- It's common. In UK veterinary records for 104,212 dogs, 4.4% (about 1 in 23) were diagnosed with an anal sac problem in a single year.4
- Breed matters. Cavalier King Charles Spaniels had 3.3 times the odds of crossbreeds, and flat-faced breeds had 2.6 times the odds of long-faced dogs.4
- Impaction dominates and surgery is rare. Impaction made up 78.6% of cases, and fewer than 1% of affected dogs had their sacs surgically removed.4
- Problems come back. Impaction recurs in 19% to 80% of dogs, often within days to weeks of the glands being emptied.1
- Cancer can be silent. In 20% to 57% of dogs with anal sac cancer, the tumor is found on a routine rectal or physical exam before any signs appear.6
What Are Anal Glands in Dogs?
The two anal sacs sit on either side of the anus, between the inner and outer anal sphincter muscles, at roughly the 4 and 8 o'clock positions.1,2 Glands in their walls make a pale yellow to straw-colored (sometimes brownish-flecked), very smelly fluid that works as a scent marker. When a dog poops, pressure from the stool squeezes a small amount out through a short duct.1,2 That's why dogs sniff each other's rear ends, and why a frightened dog sometimes releases a sudden fishy smell.
Signs of Anal Gland Problems
- Scooting (dragging the rear along the floor)3,2
- Licking or biting under the tail or at the tail base2,3
- A fishy or foul smell
- Pain when sitting or when the tail is lifted, or straining to poop3,2
- Swelling, redness or a draining sore beside the anus2
See anal gland symptoms in dogs for more detail, including other causes of scooting.
Types of Anal Sac Problems
- Impaction: the fluid thickens and the sac doesn't empty, so it becomes full and uncomfortable. This was 78.6% of cases in the UK study.4
- Sacculitis (inflammation or infection): about 12% of cases.4 The fluid may be thick, discolored (red, yellow or greenish), bloody or pus-like.1,7
- Abscess: an infected sac fills with pus and swells into a red, hot, very painful lump that can burst through the skin. About 9% of cases.4,2
- Tumors: most often apocrine gland anal sac adenocarcinoma, a cancer of older dogs. It's usually not painful in its early stages.8,5
Which Dogs Get Anal Gland Problems?
Small dogs are affected most. In the UK study, dogs under 10 kg (22 lb) had more than twice the odds of dogs 40 kg (88 lb) or heavier.4 High-risk breeds included the Cavalier King Charles Spaniel, King Charles Spaniel, Cockapoo, Shih Tzu, Bichon Frise and Cocker Spaniel, while Boxers, German Shepherds and Labradors had lower odds.4 Chihuahuas were the most affected breed in another study.9
Other contributing factors include soft stools or diarrhea, constipation, and skin allergies, which were the most common other condition in dogs with sacculitis.2,7,9 Overweight dogs are often said to be at risk, but the large UK study found no evidence of a link with obesity.4,7 See allergies in dogs and diarrhea in dogs.
Should You Express Your Dog's Anal Glands?
Healthy dogs empty their own anal sacs and don't need them expressed. Regular expression is advised only for dogs with recurring problems.2 Expressing healthy sacs routinely isn't helpful, and overly frequent or rough expression may irritate the sacs and could make problems more likely to return.10,11
If your dog does need help, a vet or vet nurse can show you what's involved, but most owners leave it to the clinic. Squeezing an infected or abscessed sac is painful, and some dogs need sedation.1 An exam also lets your vet feel the sacs for lumps, which matters in older dogs.5
How often? There's no fixed schedule. Dogs with repeated impaction often need it every few weeks to months, and vets base the timing on when signs return.10,1
Anal Sac Cancer
Apocrine gland anal sac adenocarcinoma (AGASACA) usually affects dogs around 10 years old and almost always involves one side.5 English Cocker Spaniels have about 7 times the risk of other dogs, and other spaniel breeds are also predisposed.12,5
- High blood calcium develops in about 25% of affected dogs and can cause heavy thirst, frequent urination and kidney damage.5,13
- Spread to lymph nodes inside the abdomen is common: these nodes are enlarged in about half of cases,5 and nodal spread was found in 46% of dogs in one study.14 Even tumors under 2 cm had spread in 20% of dogs in one study, against 63% of larger tumors.14
- Signs can include a lump near the anus, straining, constipation, blood in the stool or a change in stool shape, but many dogs have no signs at all.5,6
Because the tumor is often found only by feeling the sacs, ask your vet to include a rectal exam in yearly checkups for older dogs.6,14 Treatment is covered on the anal gland treatment page.
Treatment at a Glance
- Impaction: manual expression by your vet. This was used in 95% of cases in the UK study.4
- Infection: flushing the sac and placing medication directly into it, repeated every 2 to 3 weeks. In one study this cleared sacculitis in 73% of dogs.1,15
- Abscess: warm compresses, draining the abscess and, when the infection is spreading, antibiotics.1,2
- Surgery (anal sacculectomy): for repeated problems that don't respond to medical care, or for cancer.8,7
Full details, including surgical risks, are on the anal gland treatment page.
Can Anal Gland Problems Be Prevented?
There's no proven way to prevent them. Adding fiber to bulk up the stool is widely recommended so the sacs empty during defecation, but no controlled study has shown that it prevents anal sac disease.8,10 It's low risk, so it's reasonable to try with your vet's guidance. Keeping your dog at a healthy weight is good for general health, though the UK study didn't find a link between weight and anal sac problems.4 Treating underlying allergies and diarrhea is likely to help, since both are linked to sacculitis.7,9
For reader questions and answers on this topic, see reader questions about dog anal glands.
Frequently Asked Questions
What do a dog's anal glands do?
They hold a smelly fluid used for scent marking. A little is released each time the dog poops.
How do I know if my dog's anal glands are full?
Scooting, licking under the tail, a fishy smell and discomfort when sitting are the usual signs. A vet can feel the sacs to confirm it.
Do all dogs need their anal glands expressed?
No. Most dogs never need it. Routine expression is only for dogs with repeated problems.
What happens if a dog's anal glands aren't emptied?
A full sac can become impacted, then infected, and sometimes abscessed and burst. See a vet if signs last more than a day or two.
Can I express my dog's anal glands at home?
Some owners learn from their vet, but it's easy to do incompletely or too often, and an infected sac is painful. Leave it to your vet if you're unsure.
Which dogs are most likely to have anal gland problems?
Small breeds, Cavalier King Charles Spaniels, Cockapoos, Shih Tzus, Bichon Frises and other spaniels and flat-faced breeds.
Does fiber help anal gland problems?
It may, by bulking up stool, and it's low risk. But no controlled study has shown that it prevents anal sac disease.
Can anal glands be removed?
Yes, with a surgery called anal sacculectomy. It's reserved for repeated problems that don't respond to treatment, or for cancer.
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Sources and further reading
This article was rewritten and fact-checked on October 15, 2026 against current veterinary references and specialist guidelines:
- Torres SMF. Anal sac disorders. In: Small and Large Animal Dermatology Handbook, Vol. 3. University of Minnesota open textbook, 2025.
- Barnes C, Weir M, Hunter T, Ward E. Anal sac disease in dogs. VCA Animal Hospitals, May 2025.
- Rubin SI. Disorders of the rectum and anus in dogs. Merck Veterinary Manual (pet owner version), September 2024.
- O'Neill DG, Jackson C, Packer RMA, Church DB, Brodbelt DC. Non-neoplastic anal sac disorders in UK dogs: epidemiology and management aspects of a research-neglected syndrome. Veterinary Record, 2021 (VetCompass study).
- American College of Veterinary Surgeons. Anal sac tumors in dogs, June 2025.
- Cino M, Martano M. Is there anything new in canine apocrine gland anal sac adenocarcinoma? Veterinary Sciences, 2024.
- Lundberg A, Koch SN. Canine anal sacculitis: a brief review with a focus on the recent literature. Today's Veterinary Practice, September/October 2025.
- Gallagher A. Anal sac disease in dogs and cats. Merck Veterinary Manual, August 2025.
- Collins B. Anal sac diseases. Cornell Richard P. Riney Canine Health Center.
- Corbee RJ, Woldring HH, van den Eijnde LM, Wouters EGH. A cross-sectional study on canine and feline anal sac disease. Animals, 2022.
- American Kennel Club. Why is my dog scooting? September 2026.
- Science for Animal Welfare (UFAW). Cocker Spaniel: anal sac adenocarcinoma. April 2026.
- Beco L. Anal and perianal dermatosis in the dog. EVC Voorjaarsdagen, 2008. Conference proceedings hosted by IVIS (full text requires free IVIS login).
- Jones AE, Wustefeld-Janssens BG. Frequency of metastasis by tumor size in dogs with apocrine gland anal sac adenocarcinoma. Veterinary and Comparative Oncology, 2023. Summarized in Clinician's Brief.
- Lundberg A, Koch SN, Torres SMF. Local treatment for canine anal sacculitis: a retrospective study of 33 dogs. Veterinary Dermatology, 2022. Summarized in Clinician's Brief.
About this article
Last updated : fully rewritten using VetCompass and other published studies, the Merck Veterinary Manual, the American College of Veterinary Surgeons, Cornell, VCA, a University of Minnesota dermatology text and IVIS-hosted proceedings; added the research summary, signs, types of anal sac problems, breed risk, expression advice, anal sac cancer, treatment, prevention evidence, key takeaways and FAQ.
This page is for general information and is not a substitute for an exam by your veterinarian.
