Have you ever wondered where that hideous smell comes from when a skunk sprays a predator? Or why cats spew liquid on nearby tree trunks? Animal anatomy is more complex than it may appear, and the animal kingdom is replete with signals that are difficult to detect for the untrained eye.

Unbeknownst to most people, mammals such as bears, otters, possums, skunks, dogs and cats possess hidden glands called “anal sacs.” These sebaceous glands are located next to the sphincter muscles on both side of the anus, the purpose of which is to secrete a scented odor whenever the creature intentionally emits the oil, or whenever he eliminates. This is primarily used as an identification measure and territorial marking among animal species. For some animals (such as dogs and cats) the anal glands can spontaneously empty themselves in times of great stress, resulting in a pungent odor. Possums excrete the fluid when playing dead, to give off the scent of a rotting carcass, and skunks spray a stronger, more sulfurous odor when trying to defend themselves from predators. However most animals use them to mark territory and to identify themselves.

Both cats and dogs have anal sacs which are subtly expelled with every bowel movement when they pass firm stool. In instances where the cat or dog may be unwell, and the fecal matter is loose, the anal glands may not receive sufficient pressure to excrete the oil as they should. When this occurs repeatedly, the sacs swell with the oil and become uncomfortable for the pet, causing pain whenever they eliminate. One might notice that their puppy pal or cat has a swollen anal sac from the following signs:


  • Unusually behaviors include the dog or cat scooting its rear on the ground
  • Frequent licking or biting the anus region
  • Shifting weight often when seated
  • Showing discomfort when standing

NOTE: If a dog or cat is feverish, or the area is evidently red and swelling, he may have an infection or other issue that will need medical attention.

Treatment and Care

The most effective way to avoid infection and anal discomfort is to regularly attend a groomer to check the condition of the animal’s anal glands. Groomers offer anal sac expression treatments where the technician will apply pressure to the glands, causing the liquid to be released. Other treatment options allow for lancing of an abscess, or giving the pet oral antibiotics (or an antibiotic fluid injected into the swollen gland itself when necessary). If the cat or dog experiences recurring or frequent anal sac infection, some veterinarians advise performing a sacculectomy (removal of the anal sacs) in case of tumors and future complications.