When a dog's anal sacs are irritated or infected, blood flow to the area increases. The anal area becomes hot, swollen, and painful. This inflammation causes the tiny ducts that empty the anal sacs to swell shut. With the ducts swollen shut, the material within the sac dries out and hardens, first into a paste, then into a hard, gritty material. If the sac is not expressed manually or opened surgically, it bursts, creating an open, draining tract through the skin.
All dogs have two anal sacs just under the skin below the anus. Anal sacs are round little pouches approximately pea-sized in small pets and grape-sized in large pets. They secrete a thin, yellow-to-brown, foul-smelling material that is automatically dripped onto your dog's feces as he or she defecates. This material communicates information to other animals.
To find the anal sacs, lift your dog's tail, and look in the four o'clock and eight o'clock positions around the anus. Normally, sacs are barely visible because they are soft and compressible, but the opening of a single tiny duct that travels upward from each of the sacs may appear as a light dot. If the anal sacs appear obviously swollen and visibly large, or if they are hard, your pet has a medical problem and it should be addressed by your veterinarian.
Some call the anal sacs "anal glands," but the glands are actually inside the sacs and produce the material that is secreted.
Anything that causes itching, pain, or a dirty bottom can cause scooting. For example, anal sac inflammation, food allergies, and a low-fiber diet are common causes of scooting. Below, the causes of scooting are listed according to whether they cause itching, pain, or a dirty bottom.
When dogs scoot, they slide their bottoms (anus) across the floor or carpet. Scooting is not a healthy activity because it drives bacteria into your dog's skin and into the anal sac ducts. Your dog's entire bottom can become hot, swollen, and infected. Food allergies and anal sac inflammation are two common causes of scooting.
Scooting is as unhealthy for the floor as it is for your pet because it deposits bacteria, a foul odor, and sometimes fecal material, on the floor.
Anal sac inflammation and scooting is a chicken and egg scenario because inflammation caused by any factor—such as fleas, ringworm, or food allergies—can lead to scooting and scooting can lead to inflammation.
A fistula is a tract that tunnels through the skin and deeper tissues of the body. Perianal fistulas are tracts that tunnel through the tissues under your dog's tail. Perianal fistulas are common in German Shepherds and Irish Setters but are rare in other breeds.
German Shepherds and Irish Setters have tails set low and carried close to the body so that air does not circulate under the tail. Bacteria multiply in this moist, dark environment and the immune system responds to the increase in bacteria by sending in white blood cells. In dogs that develop perianal fistulas, the white blood cells are more aggressive than they should be and they attack your dog's own skin. To control the white blood cells and prevent perianal fistulas, drugs that suppress the immune system, such as Cyclosporine, are prescribed. Many dogs with perianal fistulas also have inflammatory bowel disease, a disease also due to an overly aggressive immune system. Perianal fistulas, like inflamed anal sacs, are very painful and have a foul odor.
Anal sac inflammation is caused when material cannot drain from the anal sacs. With enough swelling, the anal sac bursts open and drains. Perianal fistulas are tunneling tracts under the tail that may, or may not, involve the anal sacs. Dogs with perianal fistulas have low, clamped tails.
Both anal sac inflammation and anal fistulas cause pain and a foul odor. Both may cause pets to lick or chew the area obsessively and to snap if the area is touched.
Perineal pain is caused by anal sac inflammation, constipation, cancer, skin fold infections, anal fistulas, and clipper burns caused by grooming.
A dirty bottom is common when dogs have diarrhea, long hair, stiffness that prevents cleaning, or are obese.
Dogs lick or chew their bottoms for all the reasons listed above for scooting. In addition, female dogs in heat, incontinent females dribbling urine, and females giving birth will lick the vulva and perineum. Female pets with infection of the uterus (pyometra) may also lick the vulva.
Anal sac inflammation is common in small dogs, such as Dachshunds, Poodles and Chihuahuas, perhaps because the ducts draining their anal sacs are very tiny and easily obstructed with inflammation. It also occurs in Retrievers and Spaniels more often than in many other breeds.
Anal sac inflammation is common in the following circumstances:
Anal fistulas are common in German Shepherds and Irish Setters. These are breeds with low-set tails that keep their tails clamped down. In addition to having anatomical predisposition to anal fistulas, these breeds may have genetic immune deficiencies predisposing them to develop anal fistulas.
Anal, rectal, and perineal are adjectives that refer to the anus, rectum, and perineum. These are different areas under your dog's tail. Anal is technically limited to the anus, which is the muscular outlet of the digestive tract; and rectal refers to the last few inches of the digestive tract. Perineum is the entire area of your dog's bottom from under the tail around and down to the vulva or scrotum. Although many use the words anal, rectal, and perineal interchangeably, in this article, anal refers to the anus and the area just around it, which includes the anal sacs that empty through ducts at the anus. Perineal refers to your dog's entire bottom area.