Why do dogs’ anal glands fill up? (Causes and prevention)

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dogs anal glands are full

Key Takeaways:

  1. Various factors can cause improper emptying of the anal glands so that they fill up.
  2. While any dog can have anal gland issues, certain breeds are at higher risk.  
  3. There are several things you can try to help your dog express his anal glands and prevent them from filling up.   
  4. If your dog has swollen anal glands, is scooting, or has a fishy odor, you should contact your veterinarian.

Your dog has two tiny sacs on either side of the anus. They contain a pungent fluid that helps your pup mark his territory and lubricates his poop. If defecation doesn’t apply enough pressure to empty the glands, they will fill up with strong-smelling liquid.

When anal sacs are full, they become distended and uncomfortable for your dog. The fluid pools and may thicken thus making it harder to evacuate. If full anal glands aren’t emptied naturally or manually, they can become clogged.

In this article, we’ll share the main reasons anal glands fill up and some key risk factors. Then, we’ll offer some ways you can prevent full anal sacs. To help you help your furbaby, we’ll describe signs of full anal sacs, how to treat the condition, and when it’s time to call your veterinarian.

Gastrointestinal disease causing chronic diarrhea/soft stool

When dogs have poor digestive health that causes chronic soft stool, the feces won’t exert enough pressure on the anal glands during defecation. Over time, the anal glands fill up and may become impacted.

A short bout of diarrhea usually isn’t enough to cause a problem as long as the stool returns to normal, firm consistency. Common causes of gastrointestinal disease in dogs include inflammatory bowel disease and chronic gastritis.

Inflammatory bowel disease and other gastrointestinal disorders that lead to softer stools make it harder for your pooch to naturally express his anal glands when he poops


Obese dogs weigh at least 20% more than their ideal body weight. As they put on the pounds, they accumulate excess body fat in various places, including around the gastrointestinal tract. 

If your dog is obese, the fat in his rectum acts like padding around the anal glands. So, when he poops, the feces may not be able to put enough pressure on the sacs to express the liquid. Without natural expression, the glands fill up with fluid.

Summary: Obese dogs have extra fat padding around the anus. When they poop, the feces doesn’t get as much pressure on the glands to fully express them.

Chronic bacterial or yeast skin infections

Yeast and bacteria are the most common organisms causing skin infections in dogs. The microorganisms are ordinary residents on the skin’s surface, but in some circumstances, they multiply and cause skin disease. 

The most common symptoms of both bacterial and yeast infections are itching and red, inflamed skin. If the infection is around the anal area, the inflammation can affect the anal gland ducts causing them to swell. When anal sac ducts become swollen, it’s harder for your dog to naturally express his glands.

Dogs with chronic skin infections are prone to inflammation that can restrict the duct and cause it to fill up. 

Skin mites

Mites are tiny parasites that burrow under the skin. When they infect your dog, they cause a condition known as mange. Symptoms of mange include itching, skin irritation, and inflammation. 

Skin mites can affect the anal glands by blocking or damaging the ducts. Additionally, the skin inflammation may trigger swelling in the anal gland ducts and prevent proper emptying.

Skin mites burrow under the skin and cause inflammation that can prevent proper gland emptying.

Food allergies

Dogs may have allergies or sensitivities to food. When an allergen affects your furbaby, it can trigger inflammation in various body regions, including the skin and anal gland ducts. 

Food allergies or sensitivities can also lead to softer poop. If your pooch has consistently soft stools, there won’t be adequate pressure against the anal sacs to empty them, and they will fill up.

When dogs have food allergies, the poop is usually softer, so the anal glands aren’t effectively expressed. 

Atopic dermatitis

Allergies to environmental stimuli can cause various symptoms depending on the body system they affect. Some dogs develop digestive or respiratory symptoms. If the allergens affect the skin, it’s known as atopic dermatitis. 

Dogs with skin inflammation caused by atopic dermatitis will have itchy, inflamed skin. If the rash is around your dog’s hind end, the anal sac ducts may swell and prevent proper emptying. Over time, the anal glands fill and may become impacted.

Atopic dermatitis causes skin inflammation which can impinge on the ducts so the liquid can’t escape. 

Insufficient dietary fiber

When a dog’s stool is too soft, it usually won’t exert enough pressure to squeeze the fluid out of the sacs. Dietary fiber helps to add bulk to the feces. Conversely, a lack of fiber contributes to squishy stools. 

If your dog doesn’t have enough fiber in his diet, his poop might not be firm enough to express his anal glands naturally. As a result, the secretions continue to collect in the sacs, and they fill up.

Summary: A lack of dietary fiber can lead to softer stools that won’t press against the anal glands enough to properly express them.

Congenitally narrow ducts

Sometimes, dogs are born with anatomical abnormalities. If the congenital abnormality involves the anal glands, it can be more challenging to force fluid out of the sacs. 

While any dog can have congenitally narrow ducts, smaller breed dogs are more prone to this abnormality. Some breeds that may have narrow ducts include Chihuahuas, Lhasa apsos, and toy/miniature poodles.

Some dogs may be born with narrow ducts. Because of this, more pressure is needed to express the sacs.

Anal tumors

In dogs, apocrine(sweat) glands that produce the pungent liquid line the anal glands. When an adenocarcinoma tumor develops, the cells lining the sacs grow rapidly and can spread to other organs. These types of cancer are very aggressive.

If an anal adenocarcinoma forms in your dog, it may impinge on the ducts and interfere with proper emptying. It can also interfere with defecation. Your veterinarian will probably prescribe stool softeners until the mass is removed, but the softer poops may lead to anal gland filling.

Tumors around the anus and rectum can impinge on or occlude the duct so that the secretions can’t get out.


Dogs can develop hypothyroidism, a condition in which the body has decreased thyroxine production. When your furbaby has too little thyroid hormone, they’re prone to weight gain and food sensitivities.

As we stated above, weight gain and obesity create extra padding around the anal sacs that can interfere with proper emptying. Additionally, food sensitivities can cause skin inflammation and soft stools that further prevent expression. 

Hypothyroidism in dogs often leads to weight gain and food sensitivities that may cause soft stools or diarrhea. These effects can reduce your dog’s ability to naturally express his glands.  

Risk factors

All breeds of dogs can develop anal sac problems, but certain canines have a higher risk of issues. In a 2021 cross-sectional study of anal sac disease in dogs and cats, the authors found that certain dogs are more likely to develop anal gland disease which can result in full sacs. Their findings suggested:

  • Gender is not a significant risk factor
  • Adult dogs have a higher risk of issues than puppies
  • Small-breed dogs usually have a higher risk
  • Certain large breeds are also at risk

Another cohort study of dogs visiting veterinary clinics in the UK between January 1, 2013, and December 31, 2013, focused on breed predilections. Based on these and other studies, the breeds that are at higher risk for developing anal gland issues include:

  • Chihuahua
  • Cavalier King Charles Spaniel
  • Bichon Friese
  • Lhasa Apso
  • Toy Poodle
  • Dachshund
  • Jack Russel Terrier
  • Labrador Retriever
  • French Bulldog
  • Beagle
  • German Shepherd

Certain breeds have a higher risk of developing anal gland issues. The condition is also more likely in adults than in puppies. However, gender does not seem to be a significant factor.

Preventing dogs’ anal glands from filling up

As they say, an ounce of prevention is worth a pound of cure. The best way to avoid anal gland impaction or other issues is to prevent the sacs from filling in the first place. Fortunately, there are various things you can do to help your dog naturally express the glands so that they empty regularly. In case these measures don’t work, you should know how to recognize full glands. That way, you’ll be able to seek treatment before more serious problems develop.


Some things you can try to help your dog naturally express his anal glands so that they don’t fill up or become clogged.


You can tell your dog’s anal sacs are full when he shows certain signs:


When anal glands are full, you may be able to help your dog at home by applying warm compresses to the anal area. If this approach is ineffective, treatment may include 

  • Manual expression
  • Treat underlying conditions like infections or allergies
  • Surgical removal of chronically full glands

Summary: There are several things you can try to help prevent your dog’s anal glands from filling up and causing further problems. If the measures don’t work, you should know the symptoms of full anal sacs so that you can seek appropriate treatment for your pooch.

When should I see a vet?

If your dog shows signs that the anal glands are full, and you can’t get them to empty with warm compresses, you should contact your veterinarian. You should also schedule an appointment if you suspect an impaction. Signs of clogged ducts include:

If you’re unable to help your dog empty overly full anal glands, you should contact your veterinarian. Any time you suspect the glands are clogged, schedule an appointment.

The Final Woof

Dogs have anal glands that secrete fluid to mark territory and to help lubricate the feces. Normally, canines express their sacs during defecation, but various conditions can prevent proper emptying of the glands. Some are related to skin conditions and inflammation on the outside. Other causes are internal factors such as anatomy, tumors, and poop firmness.

Some breeds have a higher risk of anal gland problems. If your pooch is likely to have full anal glands, there are several preventive measures you can try. However, you need to know how to recognize full sacs so that you can address the situation. If you can’t help your dog at home or you suspect an impaction, take him to the vet. 

Photo of author
Dr. Libby Guise earned her DVM from the University of Minnesota in 1994. After working in private practice in Wisconsin for two years, she joined the USDA as a Veterinary Medical Officer. In 2011, Libby came home to focus on raising and teaching her adoptive daughter. She lives in Wisconsin with her daughter, husband, and two furbabies: Charis, a lab-mix rescue pup, and Chesed, a Springer Spaniel.

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