CONDITION
Anal Sac Impaction
Anal sac impaction occurs when the small scent glands located on either side of a dog's or cat's anus become filled with fluid that does not empty naturally. These glands typically release a small amount of material during defaecation, but when the ducts become blocked or the fluid thickens, the sacs can become overfull and uncomfortable. The condition is more common in smaller dogs, though it can affect any breed or size. Owners most often notice scooting—dragging the bottom along the ground—or excessive licking around the tail base. Some animals may chase their tail, have difficulty settling, or show discomfort when sitting. The area may appear swollen or red, and there may be a strong, unpleasant odour. These signs can also overlap with other conditions affecting the same region, so the pattern observed at home is part of a broader picture. This page explores the signals that may suggest impaction, what leads the glands to overfill or fail to empty, how the condition is identified during examination, and the range of approaches used to manage it—from manual expression to dietary adjustment and, in some cases, surgical removal of the glands.
Why this matters now
Anal sac impaction can occur at any age, though it tends to be recognised most often in adult dogs and cats between two and seven years old. Smaller dog breeds appear to experience the condition more frequently, which may relate to differences in sac anatomy, duct angle, or stool consistency. Animals with soft stools, low dietary fibre, or a history of skin allergies may be more prone to episodes, as may those with narrower or more tortuous duct openings.
The condition often develops gradually over days to weeks as secretions accumulate and thicken. Some animals experience a single episode that resolves after manual expression, while others develop recurring impactions over months or years. In a smaller proportion of cases, untreated impaction can progress to infection or abscess formation, which typically presents with more pronounced swelling, pain, and sometimes visible discharge or rupture of the sac wall.
Signals & patterns
Early signals
Scooting along the floor
The animal drags its bottom across carpet, grass, or other surfaces, often in short bursts. This behaviour is thought to reflect an attempt to relieve pressure or irritation around the anal opening, though it can also occur with other causes of perianal discomfort.
Licking around the tail base
Repeated or focused licking of the area just below the tail and around the anus may be observed. The behaviour tends to be more frequent or prolonged than routine grooming and can sometimes lead to dampness or reddening of the fur in that region.
Difficulty settling or sitting
The animal may appear restless when attempting to lie down, shifting position frequently or hesitating to sit fully. Some owners notice a reluctance to sit on hard surfaces or a preference for standing when at rest.
Tail chasing or biting at the base
Sudden episodes of chasing or nipping at the tail, particularly near its base, can occur. This may reflect localised discomfort that the animal is trying to address, though similar behaviour can also have other causes.
Unpleasant odour near the hindquarters
A strong, fishy or metallic smell may be noticed, particularly after the animal has been lying down or grooming. The odour comes from small amounts of anal sac fluid that may leak or be expressed inadvertently during movement or straining.
Later signals
Visible swelling beside the anus
One or both sides of the anal opening may appear raised, firm, or asymmetric. The swelling often corresponds to an overfilled or inflamed sac and may be warm to the touch if infection has developed.
Pain when defaecating or sitting
The animal may vocalise, flinch, or adopt an unusual posture during bowel movements or when pressure is applied to the hindquarters. Some animals will avoid defaecation or show signs of straining without productive passage of stool.
Discharge or bleeding near the anus
Visible fluid, pus, or blood may appear on the fur, bedding, or floor, sometimes with a sudden onset. This can indicate rupture of an overfilled or abscessed sac, which may bring temporary relief of pressure but introduces risk of secondary infection.
Reluctance to be touched around the tail
The animal may move away, tense, or show defensive behaviour when the hindquarters are approached or handled. This guarding response often reflects increased sensitivity or pain in the anal region.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis typically begins with a clinical history covering the frequency and nature of signs, stool consistency, and any previous episodes. Physical examination follows, during which the veterinary surgeon palpates the area around the anus to feel for distended, firm sacs and may perform a rectal examination to assess sac size, symmetry, and the character of any material expressed. Further investigation is reserved for cases that recur frequently, fail to respond to routine expression, or present with features suggesting infection, abscess, or an alternative underlying cause.
Physical examination
Cytology
Bacterial culture and sensitivity
Histopathology
Options & trade-offs
Management is tailored to the frequency of episodes, the animal's response to initial treatment, and the presence of complications such as infection or abscess. Many animals are managed with periodic manual expression and dietary adjustment, while others benefit from medical treatment of underlying inflammation or, in selected cases, surgical removal of the glands. The approach often evolves over time as the pattern of recurrence becomes clearer.
Manual expression
The veterinary surgeon or veterinary nurse applies gentle pressure to the distended sacs, either externally or via a gloved finger inserted into the rectum, to empty the accumulated material. This can be performed during a routine consultation and typically provides immediate relief. Some owners are taught to perform expression at home, though this requires confidence and correct technique to avoid trauma.
Trade-offs: Expression addresses the immediate impaction but does not prevent recurrence. Repeated manual emptying may be needed every few weeks or months, and over-enthusiastic or too-frequent expression can irritate the duct lining and worsen the cycle in some animals.
Dietary modification
Increasing dietary fibre—through commercial high-fibre diets, added psyllium, or cooked vegetables—can increase stool bulk and firmness, which in turn may improve natural sac emptying during defaecation. The adjustment is typically made gradually over one to two weeks to allow the gastrointestinal tract to adapt.
Trade-offs: Dietary change may reduce the frequency of impaction in some animals but has little immediate effect and may not resolve the problem entirely if anatomical or inflammatory factors are dominant. It also requires owner consistency and may not suit animals with concurrent gastrointestinal sensitivities.
Treatment of infection or abscess
When bacterial infection is present, systemic antimicrobials are prescribed based on culture results or empirical choice, often combined with anti-inflammatory medication and warm compresses if an abscess has formed. If the sac has ruptured, the wound is cleaned and allowed to heal by secondary intention, with or without surgical debridement.
Trade-offs: Antimicrobial therapy resolves active infection but does not prevent future impaction unless the underlying cause is also addressed. Abscesses may recur if the sac anatomy or secretion quality predisposes to repeated obstruction.
Anal sacculectomy
Surgical removal of one or both anal sacs is considered when impaction recurs frequently despite other measures, or when chronic infection, abscessation, or neoplasia is present. The procedure is performed under general anaesthesia and involves careful dissection to preserve the anal sphincter and nearby nerves. Recovery typically takes one to two weeks, during which stool softeners may be used to reduce straining.
Trade-offs: Sacculectomy permanently eliminates the problem in most cases, but it carries risks including faecal incontinence, infection, and damage to nerves controlling the anal sphincter, though these complications are uncommon with experienced surgeons. It is a more invasive option and is usually reserved for cases that have not responded to conservative management.
Common misconceptions
"Scooting always means the anal sacs are full and need expressing."
While impaction is a common cause of scooting, the behaviour can also result from skin irritation, allergies, intestinal parasites, perianal fistulae, or discomfort from other sources in the same region. Examination is needed to distinguish between these possibilities, and routine expression in the absence of actual impaction may do more harm than good.
"Once the sacs are expressed, the problem is cured."
Manual expression relieves the immediate distension but does not address the reason the sacs failed to empty naturally. Many animals experience repeated episodes, and understanding the underlying cause—whether anatomical, dietary, or inflammatory—helps guide longer-term management.
"All dogs need their anal glands expressed regularly as part of routine grooming."
Most dogs empty their anal sacs naturally during defaecation and never require manual expression. Routine emptying in animals without signs of impaction can irritate the ducts and may increase the likelihood of problems developing over time.
Related conditions
Anal Furunculosis (Perianal Fistulas)
Anal furunculosis can produce similar signs to anal sac impaction—scooting, licking around the tail base, and discomfort in the perianal region—but involves deeper tissue breakdown and fistula formation rather than simple gland overfilling. The two conditions occupy overlapping areas and may require examination to distinguish them.
Anal Sac Adenocarcinoma
Anal sac adenocarcinoma arises from the same glands that become impacted, and an owner noticing swelling or persistent difficulty emptying the sacs may be observing either benign impaction or, less commonly, a tumour within the gland itself. Distinguishing between the two typically requires clinical examination and sometimes biopsy.
Colitis
Colitis can cause straining, discomfort around the rectum, and scooting—signs that overlap with those of anal sac impaction. In some cases, inflammation of the colon may alter stool consistency in ways that reduce the natural emptying pressure on the anal glands, potentially contributing to impaction over time.
Anal Gland Disease
Anal gland disease describes the broader spectrum of problems affecting these glands, of which impaction is one presentation. Other patterns within this spectrum include infection, abscessation, and rupture, and understanding impaction often means considering the full range of disease that can develop in the same anatomical site.
Constipation and Megacolon
Constipation can reduce the frequency and firmness of bowel movements, which in turn may decrease the natural pressure that helps empty the anal sacs during defaecation. In some animals, chronic difficulty passing stool and recurrent anal sac impaction may be observed together, each influencing the pattern of the other.
If impaction has occurred more than once or twice, it may be useful to reflect on the pattern: whether episodes follow changes in diet, stool consistency, or periods of reduced activity, and whether there are other signs of skin or gastrointestinal sensitivity. Understanding what influences sac function in an individual animal can help shape the conversation about whether dietary adjustment, closer monitoring, or a different approach might reduce the frequency of future episodes. For animals with persistent or worsening signs despite treatment, further investigation of the sac lining, duct structure, or possible concurrent conditions may clarify the next step.
Last reviewed: 13 September 2026 · Dr Alastair Greenway MRCVS