Few dog odors are as distinctively unpleasant as the fishy smell that emanates from the rear of a dog with anal gland problems. Whether you noticed it on the couch where your dog was sitting, wafting from across the room after your dog got spooked, or intensely concentrated when your dog licks their hindquarters, the fishy odor is one of the most common reasons owners call their veterinarian. Understanding where it comes from, what it means, and when it requires treatment versus reassurance will help you respond appropriately and prevent the situation from escalating from a minor impaction into a painful abscess. The anal sacs (more accurately called anal sacs than anal glands, since the glands are the secretory lining of the sac rather than the sac itself) are paired pouches in the subcutaneous tissue at the 4 o’clock and 8 o’clock positions flanking the anus. Each sac is approximately 1-3 cm in diameter depending on breed and degree of filling, and connects to the surface of the anal canal through a small duct (approximately 2-3 mm in diameter) that opens just inside the anal margin. The lining of the sac is composed of apocrine sweat glands and sebaceous (oil-secreting) glands, the combination of which produces the characteristic secretion: an oily, yellow-gray to dark brown fluid that contains fatty acids, proteins, and compounds including trimethylamine (the same compound responsible for the fishy smell of seafood), various volatile sulfur compounds, and other odoriferous molecules. In wolves and other wild canids, anal sac secretion serves as an individual chemical signature used for territorial marking and conspecific recognition; each dog’s anal sac secretion has a unique chemical profile that conveys information about identity, sex, reproductive status, and health. The evolutionary function is not disease, and the sacs are not vestigial structures – they are an active part of canine chemical communication. The fishy odor simply reflects the organic chemistry of the secretion. Normal anal sac expression occurs during defecation: the muscles of the external anal sphincter compress the anal sacs as stool passes, expressing a small amount of secretion onto the surface of the feces. This passive expression depends on the stool being formed and firm enough to create adequate pressure. Soft, loose, or small-volume stools do not generate sufficient pressure, which is one reason dogs with chronic diarrhea or soft stools (from diet, IBD, or other causes) are at higher risk for anal sac impaction than dogs with consistent, well-formed stools. Anal sac impaction occurs when the drainage duct of one or both anal sacs becomes blocked, preventing the normal passive expression of secretions during defecation. The blocked secretions continue to accumulate, thicken, and change in consistency from a fluid to a pasty or dry, granular material as water is reabsorbed. The sac becomes progressively distended, pressing on surrounding tissue and causing discomfort. Without intervention, the impacted material provides a culture medium for bacterial colonization and the progression from simple impaction to sacculitis (infection) can occur within days to weeks. Clinical signs of anal sac impaction: scooting (the dog drags their hindquarters across the floor or grass in an attempt to apply external pressure to the distended sac), licking or chewing at the base of the tail or perineal area, turning to look at or snap at the hindquarters, discomfort when sitting (the dog sits, then immediately stands or shifts position), intermittent fishy odor particularly when the dog is resting on furniture or in their bed, and owner observation of swelling on one side of the anus. The diagnosis is confirmed on veterinary examination: the veterinarian palpates the anal sacs externally and feels distension, then performs expression. Impacted secretion is typically thick and pasty, ranging from dark brown to pale gray, and has a stronger, more concentrated odor than normal fluid secretion. Manual expression resolves uncomplicated impaction immediately; the relief for the dog is visible. Follow-up care includes identifying and addressing predisposing factors: dietary modification (increased fiber to produce firmer, bulkier stools that provide better expression pressure), weight loss for obese dogs, regular veterinary or groomer expression for dogs that impact frequently (some require expression every 4-8 weeks), and monitoring for recurrence or progression to infection. When impacted anal sac contents are colonized by bacteria, sacculitis develops. The organisms most commonly cultured from infected anal sacs include Escherichia coli, Staphylococcus pseudintermedius (the most common canine skin and mucosal pathogen), Streptococcus canis, Clostridium perfringens, Proteus mirabilis, and Pseudomonas aeruginosa in chronic or recurrent cases. The infected sac becomes inflamed: the tissue is red, swollen, and warm, the secretion becomes purulent (thick, opaque, and yellowish-gray or green-tinged), and the dog shows more prominent signs of discomfort than with simple impaction. The fishy odor is replaced or supplemented by a more putrid, necrotic smell reflecting bacterial metabolism and tissue breakdown. Treatment of anal sacculitis requires expression of the infected contents, followed by flushing the sac with diluted chlorhexidine solution (0.5-1%), sterile saline, or a diluted povidone-iodine solution to reduce bacterial load, and then infusion of an antibiotic-anti-inflammatory preparation into the emptied sac. Otomax (gentamicin 3 mg/mL, betamethasone 1 mg/mL, clotrimazole 10 mg/mL in mineral oil vehicle) instilled directly into the expressed anal sac using a small infusion tip is commonly used off-label for this purpose; it provides local antibiotic coverage (gentamicin is effective against gram-negative organisms including E. coli and Pseudomonas), anti-inflammatory effect (betamethasone reduces swelling and pain in the sac), and covers any secondary Malassezia involvement (clotrimazole). Systemic antibiotics are indicated for sacculitis with perianal tissue inflammation or systemic signs: amoxicillin-clavulanate 12.5-15 mg/kg BID for 7-14 days covers most gram-positive and gram-negative organisms; enrofloxacin 5-10 mg/kg SID or marbofloxacin 2.75 mg/kg SID provides better gram-negative coverage and is used when E. coli or Pseudomonas are suspected or confirmed on culture. Culture and sensitivity testing of the expressed contents guides antibiotic selection when initial treatment fails or infection recurs. Anal sac abscess represents the natural progression of untreated or inadequately treated sacculitis. The infected sac fills with pus under increasing pressure, causes the surrounding tissue to become devitalized, and eventually ruptures spontaneously through the perianal skin, creating a draining tract. Before rupture, the abscess appears as a painful, fluctuant (fluid-filled) swelling at the 4 or 8 o’clock position beside the anus, often visibly discolored red-brown or blue-purple as the overlying skin becomes devitalized. The dog is visibly painful – reluctant to sit, licking constantly, potentially vocalizing when the area is touched. After rupture, a draining wound with blood-tinged or purulent discharge is present. Anal sac abscess is a veterinary urgency (same-day care recommended, not a true emergency in the way that GDV or respiratory distress is, but should not be left to the next available appointment in several days). Treatment: if not yet ruptured, surgical lancing of the abscess under sedation and appropriate analgesia, followed by thorough flushing and warm soak instructions; if already ruptured, cleaning, debriding of devitalized tissue, and similar management. Systemic antibiotics (amoxicillin-clavulanate or enrofloxacin as above, extended to 14-21 days given the severity), NSAID pain management (meloxicam 0.1 mg/kg SID with food or carprofen 2.2 mg/kg BID with food), and twice-daily warm saline soaks of the perianal area until healed are the standard home care instructions. Healing time: 2-4 weeks. A dog with three or more episodes of anal sacculitis or abscess in the same sac, or bilateral recurrent disease, should be evaluated for anal sacculectomy (surgical removal). Bacterial skin infections (pyoderma) and Malassezia (yeast) overgrowth in skin folds, the perivulvar area, between digits, in the axillae (armpits), or under jowls can produce a rancid, musty, or fishy odor that the owner detects on the dog’s coat or breath. Malassezia pachydermatis (a lipophilic yeast that is part of the normal canine skin flora) produces short-chain fatty acids and polyamines as metabolic products, contributing to the characteristic “corn chip” or yeasty-musty smell of skin colonized by Malassezia; in significant overgrowth, the smell can have a sour or fishy component. Perivulvar fold dermatitis in intact or spayed females and in dogs with deep skin folds near the vulva (obese dogs, Bulldogs, Pugs) generates a particularly offensive odor as moisture, sebum, and bacteria accumulate in the fold. Diagnosis: skin cytology (tape-strip or impression smear) demonstrates increased numbers of Malassezia organisms or cocci/rods in the skin fold. Treatment: topical antifungal/antibacterial shampoo (chlorhexidine 2-4% with miconazole or ketoconazole; once or twice weekly for 4-6 weeks), daily cleaning of skin folds with chlorhexidine wipes (2%), and in severe cases oral fluconazole 5 mg/kg SID or ketoconazole 5-10 mg/kg SID for 3-6 weeks. Urinary tract infections (UTI) in dogs can produce urine with a stronger-than-normal ammonia smell or, when caused by urease-producing bacteria (Proteus mirabilis, Staphylococcus pseudintermedius), a distinctive fishy or ammoniacal odor. Urine incontinence (urethral sphincter mechanism incompetence in spayed females, neurogenic incontinence, ectopic ureter in young females) leaves urine on the perineum and inner thighs, producing a persistent urine odor that can smell fishy as the urine concentrates and ammonia volatilizes. Signs: a dog that smells like fish specifically around the rear underside rather than the perianal area, damp fur on the hindlimbs or perineum, increased thirst or urinary frequency, or a history of urinary accidents. Diagnosis: urinalysis with culture and sensitivity. Treatment: appropriate antibiotic based on culture (trimethoprim-sulfamethoxazole 15 mg/kg BID, enrofloxacin 5 mg/kg SID, or amoxicillin-clavulanate 12.5 mg/kg BID for 7-14 days for most organisms); phenylpropanolamine (Proin) 1-1.5 mg/kg BID-TID for urethral sphincter mechanism incompetence; estrogen supplementation (diethylstilbestrol 0.1-1 mg PO SID for 3-5 days then weekly) may also be used for USMI in spayed females. Periodontal disease (accumulation of dental tartar, plaque, and subgingival bacteria) produces halitosis in dogs that owners sometimes describe as fishy or rotting. The odor is produced by volatile sulfur compounds (hydrogen sulfide, methyl mercaptan, dimethyl sulfide) released by anaerobic gram-negative periodontal bacteria including Porphyromonas, Tannerella, and Treponema species. Grade 3-4 periodontal disease with deep pockets, gingival recession, bone loss, and loose teeth produces the most severe halitosis. Additional periodontal bacteria include Fusobacterium and Prevotella. Examination: yellowish-brown tartar (calculus) deposits, gingivitis (red, swollen, bleeding gum margins), and in severe cases, loose teeth or oral ulceration. Treatment: professional dental cleaning (prophylaxis) under general anesthesia with dental radiographs and extraction of non-viable teeth; home dental care (brushing with enzymatic pet toothpaste: glucose oxidase, lactoperoxidase, lysozyme daily or as often as the dog tolerates). A dog whose mouth is the source of the fishy smell should have a dental examination. Vaginitis in intact females (juvenile vaginitis, common in prepubertal females from 2 weeks to the first estrus; adult-onset vaginitis in spayed or intact adults) produces a mucopurulent vaginal discharge that has a distinct fishy to purulent odor. Juvenile vaginitis: caused by ascending colonization of the immature vaginal mucosa, typically by Staphylococcus, Streptococcus, E. coli, or Mycoplasma; most cases resolve spontaneously after the first heat cycle; treatment is generally conservative (warm saline vulvar cleaning daily, chlorhexidine wipes) unless severe or causing lower urinary signs. Adult vaginitis: associated with vaginal structural abnormalities (vestibulovaginal stricture, remnant vaginal bands), urinary incontinence, skin fold dermatitis around the vulva, or hormonal abnormalities; requires investigation of the underlying cause. Preputial discharge (smegma) in intact males has a characteristic musty-fishy smell from the accumulation of sebaceous secretion, desquamated epithelial cells, and commensal bacteria in the preputial cavity; this is normal and requires only periodic preputial cleaning if excessive. The veterinarian begins with perianal examination: visual inspection for swelling, skin discoloration, draining tracts, or discharge near the anus, followed by digital palpation of both anal sacs externally (the sacs are palpable through the perianal skin as firm, rounded structures when distended). Expression of the sac contents allows assessment of color, consistency, and odor: normal secretion is thin, pale yellow-tan to gray-brown, and fluid; impacted secretion is thick, pasty, and darker; infected secretion is opaque, purulent, and has a more putrid odor; abscess contents are frankly blood-tinged pus. Cytology of expressed contents (smear on a glass slide, Diff-Quik stained) reveals increased numbers of inflammatory cells (neutrophils) and bacteria in sacculitis, confirming infection and guiding antibiotic selection. Bacterial culture and sensitivity should be submitted in cases of recurrent infection, antibiotic treatment failure, or abscess. Proctoscopy or transrectal ultrasound may be used to evaluate the internal anatomy of the sacs and detect masses, strictures, or abscess cavities not fully accessible by palpation alone. Anal sac adenocarcinoma (a rare but important diagnosis) is an exception to the general benign course of anal gland disease and must be considered in older dogs with firm, asymmetric anal sac masses that do not resolve after expression and treatment. Anal sac adenocarcinoma (ASAC) is a malignant tumor arising from the apocrine glandular epithelium of the anal sac. It is not common – it represents approximately 2% of all canine skin tumors – but it is important because it is aggressive and frequently metastatic at the time of diagnosis. ASAC is most common in female dogs and in middle-aged to older dogs of any breed, with Cocker Spaniels, English Springer Spaniels, and German Shepherds having somewhat higher reported incidence. The tumor produces paraneoplastic hypercalcemia (caused by tumor secretion of parathyroid hormone-related protein, PTHrP) in approximately 25-50% of affected dogs; hypercalcemia causes polyuria, polydipsia, weakness, and in severe cases cardiac arrhythmias and renal failure. The owner often notices the dog licking the rear end and the veterinarian discovers a firm, sometimes asymmetric perianal mass, which may have been present for weeks to months. The tumor metastasizes most commonly to the sublumbar lymph nodes (iliac lymph nodes), which can be palpated as enlarged firm masses on rectal examination in advanced cases. Diagnosis: fine needle aspirate (FNA) cytology of the mass, confirmed by histopathology; thoracic radiographs and abdominal ultrasound for staging; serum calcium measurement. Treatment: surgical excision of the primary tumor by a board-certified veterinary surgeon (the anal sac location makes complete excision technically challenging, and wound dehiscence is a risk); adjuvant radiation therapy (5 fractions of 8-10 Gy given weekly using 3D-conformal or IMRT technique) for incompletely excised primaries or sublumbar node disease; mitoxantrone 5 mg/m2 IV every 3 weeks or toceranib phosphate (Palladia) 2.5-3.25 mg/kg PO Monday-Wednesday-Friday as chemotherapy for metastatic disease; median survival time with surgery plus radiation is 18-24 months; with surgery alone, approximately 12-15 months. For a dog with a first episode of anal sac impaction that has been expressed by the veterinarian, the following measures reduce the risk of recurrence: If my dog smells like fish, I should squeeze or “express” the anal glands myself at home regularly to prevent problems. Routine home expression of anal sacs that are not causing problems is not recommended and may actually increase the risk of inflammation, trauma to the duct, and scarring. The anal sacs should be expressed when they are causing signs (scooting, licking, odor, swelling), not on a fixed calendar schedule by someone with limited training. Groomers who routinely express anal sacs externally on every dog at every grooming visit are performing an unnecessary procedure on dogs whose sacs are not impacted. Veterinary expression, performed when clinically indicated, using internal digital palpation, is more complete and less likely to cause duct trauma than external “pinching.” If your dog requires frequent expression, work with your veterinarian to address the underlying predisposing factors rather than simply expressing on schedule indefinitely. A fishy smell from a dog always comes from the anal glands and always means the same thing. While the anal sacs are the most common source of a fishy odor, the same smell can come from pyoderma and Malassezia overgrowth in skin folds, vaginal discharge in females with vaginitis, urinary incontinence with urine accumulation on the perineum, dental disease, and less commonly from kidney disease (in which volatile amine compounds are exhaled and also present in urine). Localizing the smell to the rear end versus the breath, the perineum versus the perianal area, and whether it is constant or only present at certain times helps distinguish anal gland from other sources. A dog whose fishy smell does not resolve after anal sac expression, whose sacs appear normal on examination, or who has additional signs (increased thirst and urination, skin rash, vaginal discharge) has a different underlying cause that requires investigation. Anal gland problems in dogs are caused by diet and can always be cured with a raw diet or specific food. Diet is one of several factors that influence anal sac health, primarily through its effect on stool consistency and firmness. A diet that produces firmer stools (higher fiber content, appropriate moisture) improves passive anal sac expression and reduces impaction frequency in some dogs. However, diet alone is rarely curative for dogs with structural duct abnormalities, significant obesity-related compression, hypothyroidism, severe atopy, or anatomically small anal sac openings. Raw diets produce firmer stools (from the higher bone content) in some dogs, which can help, but the benefit is from stool firmness rather than any specific anti-inflammatory property of raw meat. Dogs with food hypersensitivity causing perianal dermatitis and secondary anal sac problems do genuinely benefit from a food elimination trial with a novel protein or hydrolyzed protein diet, but this addresses one specific mechanism and does not apply to all dogs with anal gland issues. The most common reason for a sudden fishy smell is spontaneous anal sac expression – the dog’s anal sacs released their contents during a moment of fear, excitement, or straining. This deposits the intensely fishy-smelling secretion onto the dog’s fur and can transfer to furniture or your clothing. The smell often lingers until the dog is bathed. If the dog did not visibly scoot or express distress, a bath resolves the immediate odor, but a veterinary examination to assess the anal sacs is appropriate to prevent a true impaction from developing. The anal sac secretion is oily and fat-soluble, so a regular pet shampoo is often insufficient. Bathe your dog with a degreasing or deodorizing shampoo (Dawn dish soap diluted 1:3 with water works well as an initial degreasing wash before using pet shampoo; or a veterinary chlorhexidine-based shampoo like Douxo S3 Calm). Focus on the tail base, perineum, and hindlimbs where the secretion is most concentrated. Rinse thoroughly. For furniture or fabric, enzymatic pet odor eliminators (products containing protease and lipase enzymes, such as Nature’s Miracle, Anti-Icky-Poo, or Biokleen Bac-Out) break down the odor compounds more effectively than general cleaners. Home expression is possible after proper instruction from your veterinarian, but it is not recommended for routine preventive use. External expression (pinching the perianal skin from outside) is less complete than internal expression and may leave secretion in the sac. Incorrect technique can cause trauma to the duct, incomplete expression, or exacerbation of a developing infection. If your dog requires very frequent expression (more often than every 6-8 weeks), your veterinarian can demonstrate safe technique; otherwise, veterinary or trained-groomer expression when clinically indicated is preferable to routine home expression on a calendar basis. Scooting (dragging the hindquarters on the ground) combined with a fishy odor is the classic presentation of anal sac impaction. The dog is attempting to relieve the pressure and discomfort of distended anal sacs by applying external friction. This combination virtually always means a veterinary visit and manual expression are needed. If the dog is also licking the area excessively, seems painful when sitting, or you can see or feel swelling beside the anus, the impaction may have progressed to sacculitis or early abscess formation and same-day care is appropriate. There is no universal correct answer. Dogs whose sacs express passively during every normal defecation (most dogs on high-fiber diets with consistent stools) require no manual expression at all. Dogs that are impacted periodically should be expressed when they show signs (scooting, odor, licking) rather than on a fixed schedule. Dogs that impact frequently despite dietary management may need expression every 4-8 weeks. Your veterinarian will advise you based on your individual dog’s anatomy, diet, stool quality, and history. In female dogs, a fishy smell associated with self-licking can come from several sources: anal sac impaction or infection (the most common), vaginal discharge from vaginitis (juvenile or adult-onset), urinary incontinence with urine on the perineum, or Malassezia overgrowth in the perivulvar skin folds. The location the dog is licking (perianal vs. vulvar region), the character of any discharge (anal sac secretion vs. vaginal discharge vs. urine), and any concurrent signs help distinguish the source. A veterinary examination is the most direct way to determine the cause and appropriate treatment. For many dogs, the underlying predisposing factors can be managed well enough to dramatically reduce the frequency of impaction: high-fiber diet, weight loss, allergy management, and regular professional expression reduce recurrence in most dogs. For dogs with recurrent anal sacculitis or abscess in the same sac despite optimal medical management, or dogs who require expression so frequently (every 2-3 weeks) that the intervention itself is causing duct trauma and inflammation, anal sacculectomy (surgical removal of the affected sac) by a veterinary surgeon is a permanent solution. Bilateral sacculectomy carries a risk of fecal incontinence from inadvertent damage to the external anal sphincter; this risk is lower when the procedure is performed by an experienced surgeon with good anatomical technique, but it is a consideration that should be discussed preoperatively. For more guides on keeping your dog healthy, browse all our Dog Health articles.
Dog Smells Like Fish: Anal Glands, Causes, and What to Do
Small Animal Internal Medicine and Dermatology
This article is reviewed for clinical accuracy. A persistent fishy odor that is accompanied by scooting, excessive licking of the hindquarters, swelling or redness near the anus, changes in defecation, or purulent discharge warrants a veterinary examination. Impacted or infected anal glands are a treatable condition but do not resolve without intervention.
Key Takeaways
Anal Gland Anatomy: Why the Fishy Smell Exists
Anal Sac Impaction
Anal Sacculitis (Infected Anal Glands)
Anal Sac Abscess
Other Causes of Fishy Odor in Dogs
Pyoderma and Skin Fold Infections
Urinary Tract Infection and Incontinence
Dental Disease and Oral Odor
Fishy Smell from the Vagina or Prepuce
Breed Predisposition and Risk Factors
Factor
Effect on Anal Gland Problems
Most Affected Breeds
Small breed / toy breed body size
Sac ducts are proportionally smaller, impaction more likely
Chihuahua, Yorkshire Terrier, Toy Poodle, Miniature Dachshund, Maltese, Bichon Frise
Obesity
Increased adipose tissue compresses sac ducts; reduced stool pressure from reduced activity
All breeds; particularly Labrador, Beagle, Cocker Spaniel
Soft or loose stools
Insufficient pressure to passively express sacs during defecation
Dogs with IBD, food sensitivity, dietary indiscretion, or low-fiber diets
Skin or environmental allergies (atopy)
Perianal inflammation from pruritus and self-trauma; duct edema from dermatitis
West Highland White Terrier, Golden Retriever, Labrador, Cocker Spaniel
Food hypersensitivity
Chronic soft stools reduce passive expression; perianal dermatitis possible
Labrador, Cocker Spaniel, German Shepherd, Boxer
Hypothyroidism
Sebum accumulation and poor sac secretion quality predispose to impaction
Doberman, Golden Retriever, Irish Setter, Cocker Spaniel
Anal sac anatomy variants
Abnormally narrow ducts or deep sac positioning increases impaction frequency
Identified in individual dogs of any breed at any age
Diagnosis and Veterinary Workup
Anal Sac Adenocarcinoma: When the Fishy Smell Has a More Serious Cause
Red Flags: When a Fishy-Smelling Dog Needs Same-Day Veterinary Care
Home Management and Prevention
Age-Specific Considerations
Puppies (Under 1 Year)
Adult Dogs (1-8 Years)
Senior Dogs (8+ Years)
Myths About Dogs Smelling Like Fish
Frequently Asked Questions About Dogs Smelling Like Fish
Why does my dog suddenly smell like fish?
How do I get the fishy smell off my dog?
Can I express my dog’s anal glands myself?
What does it mean when my dog scoots and smells like fish?
How often should anal glands be expressed in dogs?
Why does my female dog smell like fish when she licks herself?
Can anal gland problems in dogs be permanently fixed?
Reviewed by a Licensed Veterinary Doctor (DVM)
Myth
Fact
Myth
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