Dogs have two small sacs just beneath the skin on either side of the anus, and they naturally fill with a strong-smelling fluid between bowel movements. That’s normal. The real question most owners are asking is why these glands stay full, becoming swollen, uncomfortable, or impacted instead of emptying on their own. The answer usually comes down to stool consistency, anatomy, allergies, or some combination of the three.
How the Glands Are Supposed to Work
Each anal sac produces a pungent, oily liquid that likely serves as a territorial scent marker. It’s the reason dogs sniff each other’s rear ends: they’re reading chemical information unique to that dog. Under normal circumstances, when a firm stool passes through the anus during a bowel movement, it physically presses against both sacs and squeezes a small amount of fluid out onto the surface of the stool. Most dogs go their entire lives without any issues because this built-in pressure system works reliably every time they defecate.
Problems start when something disrupts that mechanical squeeze. The fluid keeps being produced whether or not it gets released, so the sacs gradually fill, the secretion thickens, and what was once a thin liquid becomes a paste that’s even harder to push out. That cycle of filling and thickening is at the core of nearly every anal gland problem.
Soft Stools Are the Most Common Culprit
Firm, bulky stool is what creates enough outward pressure to compress the glands on the way out. When a dog has chronically soft stools, whether from a low-fiber diet, food sensitivities, or recurring digestive upset, the stool simply slides past the sacs without pressing hard enough to empty them. Diarrhea makes the problem worse because there’s almost no solid mass to create pressure at all.
This is why fiber is the first thing most vets recommend. Insoluble fiber (like wheat bran or cellulose) adds physical bulk to the stool, making it firmer and more effective at squeezing the glands during defecation. Products marketed specifically for anal gland health typically contain cellulose for exactly this reason. Canned pumpkin is a popular home option because it provides both soluble and insoluble fiber. Psyllium is another useful supplement: despite being a soluble fiber, it resists quick fermentation and maintains a gel-like consistency all the way to the colon, which helps firm up loose stools in dogs with chronic diarrhea.
Allergies and Inflammation
Food allergies and environmental allergies are an underappreciated driver of recurring anal gland problems. Allergic reactions can cause low-grade inflammation in the tissue surrounding the anal sacs and the tiny ducts that drain them. When those ducts swell, the opening narrows, and even normal-consistency stool may not generate enough force to push the thickened fluid through a partially blocked exit. Allergies also frequently cause softer stools or intermittent digestive issues, compounding the mechanical problem.
If your dog’s anal glands fill up repeatedly despite a good diet and firm stools, an underlying allergy is worth investigating. Dogs with allergies often show other signs too: itchy ears, paw licking, or skin irritation, though some dogs present with anal gland issues as their primary symptom.
Breeds That Are More Prone
Anatomy plays a significant role. A large-scale study from the Royal Veterinary College found clear breed differences in anal sac disorder risk. Cavalier King Charles Spaniels and King Charles Spaniels had roughly 3.3 times the risk of crossbred dogs. Cockapoos had about 2.6 times the risk. Shih Tzus, Bichon Frises, and Cocker Spaniels were also at elevated risk.
Broader breed types showed patterns too. Flat-faced (brachycephalic) dogs had 2.6 times the risk compared to long-faced dogs. Spaniel types had about twice the risk, poodle types about 1.5 times, and dachshund types about 1.4 times. On the other end of the spectrum, Boxers, German Shepherds, Lurchers, Staffordshire Bull Terriers, Border Collies, and Labrador Retrievers all had lower-than-average risk.
The reasons likely involve the size and positioning of the sacs relative to the anal sphincter muscles. Smaller dogs tend to have proportionally smaller ducts that clog more easily, and variations in how the sacs sit anatomically can make natural expression less efficient regardless of stool quality.
Body Weight Matters
Overweight and obese dogs are more likely to have recurring anal gland problems. Excess fat tissue around the hindquarters can change the position of the sacs or reduce the mechanical pressure that the sphincter muscles exert during defecation. Overweight dogs also tend to be less active, and reduced muscle tone in the pelvic area can further weaken the natural expression mechanism. For dogs that carry extra weight and have chronic gland issues, weight loss alone sometimes resolves the problem.
Signs the Glands Are Too Full
The classic sign is scooting: dragging the rear end along the floor or ground. But that’s not the only indicator. Dogs with overfull or impacted glands often lick or bite at the area around the tail base, strain or show discomfort during bowel movements, or seem reluctant to sit down. You might notice a fishy smell that’s stronger than usual.
When impaction progresses, you can sometimes feel hard masses on either side of the anus. If bacteria get into the trapped fluid, the sacs can become infected or abscessed. An abscess causes visible swelling, redness or purple discoloration of the skin near the anus, and significant pain. Left untreated, abscessed sacs can rupture through the skin, creating an open wound that drains pus and blood. This is painful and requires veterinary treatment, so catching the early signs of overfilling matters.
Manual Expression and Its Limits
When glands are impacted, a vet can manually squeeze out the contents. This provides immediate relief, but it’s a treatment for the symptom, not the cause. Some dogs with chronic issues end up on a schedule of regular manual expression every few weeks.
It’s worth knowing that improper technique can cause bruising, pain, or even damage to the sac walls, which worsens inflammation and can make the cycle of filling worse over time. If your vet recommends routine expression and you want to learn to do it at home, get hands-on instruction first. For dogs with healthy glands that empty normally, routine expression isn’t necessary and can actually irritate the tissue, potentially creating a problem where none existed.
Reducing How Often the Glands Fill
The most effective long-term strategy targets stool quality. Adding insoluble fiber to bulk up stools is the simplest starting point. Canned plain pumpkin (not pie filling) mixed into food, a cellulose-based supplement, or wheat bran sprinkled over meals can all help. Start with small amounts and increase gradually to avoid gas or loose stools from the sudden dietary change.
If allergies are involved, identifying and removing the trigger, whether it’s a specific protein in food or an environmental allergen, can reduce the inflammation that narrows the ducts. An elimination diet supervised by a vet is the standard approach for food allergies. Maintaining a healthy body weight removes another contributing factor, and regular exercise supports overall muscle tone in the pelvic area.
For dogs with anatomical predispositions (small breeds, flat-faced breeds, spaniels), these measures may reduce the frequency of problems without eliminating them entirely. Some of these dogs will need periodic manual expression as part of their routine care, and in rare, severe cases where impaction or infection keeps recurring despite all other interventions, surgical removal of the anal sacs is an option that permanently resolves the issue.