Anal Sac Disease in Dogs: Signs, Causes and When to Call

Every dog has two small scent pouches tucked beside the anus, and most of the time nobody gives them a second thought. Anal sac disease starts when those pouches stop emptying. The fluid thickens and plugs them (impaction), bacteria move in (infection), pus builds up (an abscess), or, much less often, a tumor grows in the sac wall.

The classic first sign is scooting: your dog dragging its bottom across the floor. Licking under the tail, a bad smell and pain when sitting often follow. A painful swelling, or blood or pus beside the anus, means a same-day call to your vet. And skip squeezing the sacs yourself: most dogs never need it, and the sacs are easy to hurt.

It's a common problem. In a UK study of more than 100,000 dogs seen by primary-care vets, about 4.4% were diagnosed with a non-cancer anal sac disorder in a single year (O'Neill et al., Veterinary Record, 2021).

What Are Anal Sacs?

The anal sacs (often called anal glands) are two small pouches on either side of the anus, at about the 4 o'clock and 8 o'clock positions. Glands in the sac walls make a strong, foul-smelling fluid that collects inside, and a tiny duct carries it to an opening just inside the anus.

That fluid is a scent signature (the sacs are related to a skunk's scent glands), which is why dogs sniff each other's rear ends. A little is squeezed out each time a firm stool passes, so the sacs normally empty without anyone noticing.

A frightened dog can suddenly release its sacs, leaving a strong smell in the car or the exam room, and some dogs leak a little while resting. Neither is a disease on its own, but mention a leaky dog to your vet. Cats have anal sacs too, though problems are uncommon in cats.

Impaction, Infection, Abscess or Tumor?

The first three often follow each other: a sac that stays full is more likely to get infected, and an infected sac with a blocked duct can turn into an abscess. Tumors are a separate story.

Impaction

Impaction is the most common anal sac problem. The ducts get inflamed, the secretion thickens, and the swollen sac makes passing stool uncomfortable. It is more likely with:

• Small size. Small breeds are more often affected. One large UK study found higher odds in Cavalier King Charles Spaniels, Cockapoos, Shih Tzus, Bichon Frises and Cocker Spaniels, and in flat-faced breeds.
• Soft stool. Loose stool doesn't press the sacs hard enough to empty them. Constipation can cause trouble too.
• Extra weight. Overweight dogs have poorer muscle tone around the anus, so the sacs empty less well.
• Skin disease and allergies. Dogs with skin problems seem more prone.
• Overproduction. Some dogs make more secretion than they can empty.

Infection (Anal Sacculitis)

Bacteria that would normally be flushed out with each bowel movement stay and multiply in a sac that doesn't empty. An infected sac hurts more than a simple impaction, and the fluid can turn bloody.

Anal Sac Abscess

When an infected sac's duct is blocked, pus has nowhere to go. The result is a painful, red, hot swelling on one or both sides of the anus. If it bursts, greenish-yellow or bloody pus drains through a hole in the skin beside the anus, and owners often mistake it for bleeding from the rectum.

A burst abscess can leave a draining tract. Vets tell this apart from perianal fistula, a different chronic disease with deep, foul-smelling wounds around the anus that is most common in German Shepherds.

Signs of Anal Sac Problems in Dogs

• Scooting, often the first sign
• Licking or biting under the tail or at the base of the tail
• A bad smell that lingers on your dog or its bed
• Straining or discomfort when pooping (see signs of constipation in dogs)
• Not wanting to sit, or sitting lopsided
• Tail chasing
• Snapping or growling when the tail is touched, even in a gentle dog
• Swelling, redness, blood or pus beside the anus

Why Is My Dog Scooting?

Full or inflamed anal sacs are the usual suspect. Other causes include:

• Tapeworms and other parasites. Look for rice-like segments around the anus, in the stool or on bedding; your vet may check a stool sample.
• Irritation after grooming. Clipper burn, small nicks or a new shampoo or spray can make the area itchy.
• Allergies and food sensitivities. Itchy skin can include the rear end, and loose stool keeps the sacs from emptying.
• Itchy skin elsewhere or back pain. If the sacs are empty and the scooting carries on, your vet will look for another cause.

An occasional scoot after a muddy walk is no cause for worry. Scooting that keeps happening deserves a vet visit.

When to Call the Vet

Call now (same day):

• A swollen, red, hot or very painful area beside the anus

• Blood or pus draining from beside the anus, or a hole in the skin there (a burst abscess)
• Straining without passing stool
• A lump near the bottom together with vomiting, weakness, not eating, or a lot of drinking and peeing

See your vet soon (within a day or two):

• Scooting more than once in a while, or licking under the tail a lot
• A bad smell from the rear end that keeps coming back
• Discomfort when sitting or pooping
• Any new lump near the anus, even a painless one

Mention at your next visit:

• Ask for an anal sac check at routine exams, especially for older dogs
• A dog that leaks fluid when relaxed or scared
• Repeat anal sac trouble, so you can plan prevention together

Should You Express Your Dog's Anal Glands at Home?

No. Most dogs never need their anal sacs emptied by hand, because the sacs are built to empty when firm stool passes. Squeezing them when they aren't full, or too hard, can damage them (AKC), and it does nothing about an infection or a tumor.

A dog with symptoms needs an exam, not a squeeze: a vet can feel the sacs from inside and tell an impaction from an infection or a lump. Some dogs with repeat problems do benefit from regular emptying, but that is a job for your vet team or a groomer your vet trusts, and only when your vet says your dog needs it. Groomers are often the first to spot a swelling under the tail, so pass that on to your vet.

Not sure whether the glands are the problem? Our guide on how to tell if a dog's anal glands may need attention walks through the signs.

How Vets Diagnose and Treat Anal Sac Disease

Diagnosis. Most cases are diagnosed on a gloved rectal exam, when the vet feels each sac and tries to empty it. Impacted secretion is thick and brown; infected fluid may be bloody or contain pus, and repeat infections may mean a culture. A sac that is firm, enlarged and won't empty raises concern for a tumor and calls for more tests.

Treatment depends on the problem, and your vet chooses any medicines:

• Impaction: the vet empties the sacs by hand, or flushes them under sedation if the contents are too hard or the dog is too sore.
• Infection: emptying and flushing, sometimes medicine placed into the sac, plus antibiotics and pain relief when needed.
• Abscess: an abscess that hasn't burst may need to be lanced and drained; a burst one is cleaned and treated for infection and pain, often with a cone to stop licking and your vet's instructions for care at home.
• Follow-up: some dogs need a recheck to confirm the sacs are emptying and the infection is gone.

When Surgery Is the Answer

If treatment keeps failing or problems keep coming back, the vet may recommend removing the sacs (anal sacculectomy), sometimes through a board-certified surgeon. Few dogs get there: in the UK study, fewer than 1% of dogs with non-cancer anal sac disorders had it. Dogs don't need their anal sacs, and life without them is normal.

The closed technique, which removes the sac intact, is generally preferred because it has the lowest complication rate. The main risk is fecal incontinence, because the nerves that control the anal sphincter run close to the sacs. Loose stools or poor bowel control usually settle within a few weeks and are rarely permanent. A draining tract can return if sac tissue is left behind.

Anal Sac Tumors (Adenocarcinoma)

The most common anal sac tumor is apocrine gland anal sac adenocarcinoma, a cancer of the glands in the sac wall. According to the American College of Veterinary Surgeons, it is uncommon, almost always on one side, seen at an average age of about 10, and more common in spaniels. Males and females are affected about equally.

These tumors are often painless and don't cause the scooting and licking that impaction does, which is why vets check the sacs during routine exams. Signs can include:

• A swelling beside the anus, or a mass the vet feels on a rectal exam
• Constipation or straining
• Blood in the stool
• Drinking and peeing more, vomiting, poor appetite and tiredness

That last group comes from high blood calcium (hypercalcemia of malignancy). About 1 in 4 dogs with this tumor have it, and high calcium can damage the kidneys (see signs of kidney failure in dogs).

The cancer can spread even while the tumor is small, most often to lymph nodes deep in the abdomen, which are enlarged in about half of cases. Vets usually check with a needle sample of the lump, bloodwork for calcium and kidney values, chest x-rays and an abdominal ultrasound.

Treatment. Surgery is the mainstay and the only treatment shown to affect survival: the affected sac comes out, plus enlarged lymph nodes through a separate abdominal incision if needed. Dogs with high calcium or kidney trouble may need IV fluids and medications first, and chemotherapy or radiation afterward may help some dogs live longer.

The outlook depends on the tumor's size, calcium level and lymph node involvement, so early detection matters. A veterinary oncologist can talk you through the options; our cancer questions answered post covers the basics.

Can You Prevent Anal Sac Problems?

Not always, but you can stack the odds:

• Keep your dog lean. Extra weight is a known risk factor.
• Look after stool quality. Firm stool empties the sacs. Report ongoing diarrhea or soft stool to your vet.
• Treat itchy skin. Getting allergies under control may mean fewer flare-ups (see atopic dermatitis in dogs).
• Ask about fiber. Vets sometimes recommend extra fiber to bulk up stool. A small 2025 trial in 35 dogs found fewer repeat impactions with a fiber and probiotic chew (Salichs et al., Veterinary Dermatology), but the evidence is limited, so let your vet choose the diet or product.
• Ask for a sac check at routine exams, especially as your dog gets older.

Questions to Ask Your Vet

• Is this impaction, infection, an abscess, or something else?
• Is something underneath it, like allergies, soft stool or weight, that we should treat?
• Does my dog need the sacs emptied regularly, or should we let them empty on their own?
• If this keeps coming back, when would you consider surgery?

Sources

• Merck Veterinary Manual: Anal Sac Disease in Dogs and Cats
• Merck Veterinary Manual (pet owner version): Disorders of the Rectum and Anus in Dogs
• American College of Veterinary Surgeons: Anal Sac Tumors in Dogs
• VCA Animal Hospitals: Anal Sac Disease in Dogs
• O'Neill DG et al. Non-neoplastic anal sac disorders in UK dogs: epidemiology and management aspects. Veterinary Record, 2021
• Corbee RJ et al. A cross-sectional study on canine and feline anal sac disease. Animals, 2021
• Salichs M et al. Efficacy of an oral chew containing fibre and Bacillus velezensis C-3102 in the management of anal sac impaction in dogs. Veterinary Dermatology, 2025
• American Kennel Club: Why Is My Dog Scooting?
• PetPlace: Anal Sac Disease in Dogs
• Greencross Vets: Anal Glands

This article is for general information and is not a substitute for advice from your veterinarian.