Dogs release their anal glands primarily during bowel movements, when the pressure of passing stool squeezes two small sacs located just inside the anus and pushes out a strong-smelling fluid. This fluid serves as a chemical signature, carrying information about the individual dog that other dogs can read through scent. It’s also why dogs are so interested in sniffing each other’s rear ends and investigating other dogs’ feces.
What Anal Glands Actually Do
Every dog has two anal sacs, one on each side of the anus at roughly the four o’clock and eight o’clock positions. These grape-sized pouches produce an oily, pungent secretion that coats the stool as it passes. The fluid is loaded with volatile compounds, including sulfur-based chemicals that act as pheromones, and other substances unique to each dog.
This secretion functions as a biological ID card. It communicates a dog’s sex, reproductive status, and individual identity to other dogs. Some compounds appear to be species-specific markers found in all dogs but not in other animals, helping with species recognition. Other compounds vary between individuals, creating a unique chemical profile. This is why dogs sniff each other’s backsides when they meet: they’re gathering detailed social information from residual anal gland secretion.
The secretions also play a role in territorial marking. When a dog defecates, the fluid released onto the stool leaves a scent marker that persists in the environment long after the dog has moved on. This territorial function is shared across many carnivore species, from wolves to weasels.
How Normal Release Works
The standard mechanism is simple: when a dog passes a firm, well-formed stool, the stool presses against the anal sacs on its way out. That physical pressure squeezes the fluid through a tiny duct that opens just inside the anal opening. The whole process happens automatically, and most dog owners never notice it because the secretion is deposited directly onto the stool in small amounts.
This is why stool consistency matters so much for anal gland health. Soft or loose stools don’t create enough pressure to fully empty the sacs. Over time, fluid accumulates and thickens, making it harder to express naturally. A diet with adequate fiber helps produce firmer, bulkier stools that apply the right amount of pressure during bowel movements.
Sudden Release From Fear or Stress
If you’ve ever noticed your dog emit a sudden, intensely fishy smell during a vet visit, a thunderstorm, or a startling encounter, that’s an involuntary anal gland release. Acute fear or stress can cause the muscles around the anal sacs to contract, squirting out the contents all at once rather than gradually during defecation.
This is similar to how many animals release strong-smelling secretions when threatened. The skunk’s spray is the most famous example, and while a dog’s anal gland discharge is far less dramatic, it operates on the same principle. The sudden burst of smell may function as an alarm signal to other dogs, though the exact purpose in these situations isn’t fully understood. What’s clear is that it’s involuntary, and it’s normal. A single stress-related release isn’t a sign of a health problem.
When the Glands Don’t Empty Properly
Problems start when the sacs don’t empty on their own. The fluid builds up, thickens, and becomes difficult to pass through the narrow duct. This is called impaction, and it’s the most common anal gland issue in dogs. Left untreated, impaction can progress to infection, and eventually to an abscess that may rupture through the skin near the anus.
Signs that your dog’s anal glands aren’t emptying properly include:
- Scooting: dragging the rear end along the ground
- Excessive licking or biting at the base of the tail or rear end
- A persistent fishy odor that doesn’t go away after a bowel movement
- Swelling or redness near the anus
- Straining or discomfort during defecation
If an abscess forms, you may notice a painful, swollen area beside the anus that can leak bloody or pus-like discharge. This requires prompt veterinary treatment.
Dogs Most at Risk
Small dogs are disproportionately affected by anal gland problems. In veterinary surveys, about 60% of reported cases involve dogs under 10 kilograms (roughly 22 pounds). Small breeds may have narrower anal sac ducts that clog more easily, and they may also have weaker anal sphincter muscle tone, which reduces the natural squeezing action during defecation.
Specific breeds reported most often with anal sac disease include Chihuahuas, French Bulldogs, Jack Russell Terriers, Lhasa Apsos, and Beagles. But larger breeds aren’t immune. Labrador Retrievers and German Shepherds also show up frequently. In German Shepherds, the anal sacs sit deeper in the tissue near the rectum than in most breeds, which may make them more prone to impaction. Labradors are overrepresented in cases requiring surgical removal of the glands.
Obesity is another significant risk factor. Excess fat around the anus can compress the anal sac ducts, trapping the secretion inside. Dogs with chronic diarrhea or ongoing skin problems are also more likely to develop anal sac disease, since both conditions interfere with the normal emptying process.
Keeping Anal Glands Healthy
For most dogs, the best prevention is a diet that produces firm, well-formed stools. Fiber is the key ingredient here. It adds bulk to the stool, which increases pressure against the anal sacs during bowel movements and supports natural expression. If your dog has recurring issues, your vet may suggest a higher-fiber diet or a fiber supplement to achieve the right stool consistency.
Routine manual expression (having someone squeeze the glands by hand) is a common grooming service, but it’s generally unnecessary for dogs whose glands empty normally. For dogs with chronic impaction, periodic manual expression can prevent fluid buildup from reaching the point of infection. Your vet can show you what a healthy expression schedule looks like for your specific dog.
Maintaining a healthy weight also helps. Since perianal fat compresses the ducts and blocks drainage, keeping your dog lean reduces one of the most controllable risk factors for anal gland problems.