Common Causes (Ranked by Likelihood)
Cats have two anal glands (also called anal sacs) at the 4 and 8 o'clock positions around the anus. They produce a fishy, musky secretion used for territorial marking. Normally expressed during defecation, these glands can leak spontaneously when a cat is stressed, frightened, or has soft stools that don't provide enough pressure. Impacted glands (not emptying properly) cause the cat to scoot, lick excessively at the rear, or emit a fishy smell from their general vicinity — especially where they sit.
UTIs cause abnormally strong, fishy-ammonia urine. Cats spread urine smell throughout their coat during grooming — particularly on paws, belly, and face. Female cats are more prone to UTIs. The smell is often described as fishy-ammonia rather than pure fish. Associated signs include increased urination frequency, straining, blood in urine, and genital licking.
Severe dental disease — particularly periodontitis with necrotic tissue — produces a distinctly fishy or rotten smell on a cat's breath. As cats groom themselves extensively, bad breath transfers to their coat, creating a fishy odor that seems to come from the fur. Dental disease is extremely common in cats over 3 years old — over 70% have some degree of periodontal disease.
Cats eating predominantly fish-flavored food naturally have fishy-smelling breath, urine, and sometimes coat. Fish contains trimethylamine oxide which converts to trimethylamine — the compound responsible for fish odor — during digestion. High-fish diets also produce strongly-smelling waste that can linger on fur after litter box use. This is the most benign cause — but fish-heavy diets long-term have nutritional drawbacks.
Pyometra is a life-threatening uterine infection affecting intact (unspayed) female cats. An open pyometra produces a foul-smelling vaginal discharge that can have a fishy or putrid character. This is a veterinary emergency — cats with pyometra can deteriorate rapidly. Any intact female with a fishy discharge, lethargy, increased thirst, or swollen abdomen requires immediate veterinary attention.
How to Fix It
Anal Gland Expression
$25-50 at vetFor anal gland leaking — do not attempt at home without instruction.
- 1Book a vet or groomer appointment for anal gland expression — a simple procedure taking a few minutes.
- 2The vet manually expresses the glands by applying gentle pressure. You can ask your vet to show you how for future home maintenance.
- 3For cats with recurring issues: discuss dietary changes — higher fiber diets produce firmer stools that naturally express the glands during defecation.
- 4Impacted or infected glands require more intervention — the vet may flush the glands or prescribe antibiotics.
- 5Cats that repeatedly have anal gland issues may benefit from surgical removal of the glands (anal sacculectomy).
Treat UTI
$100-200Requires vet diagnosis — don't treat with home remedies.
- 1Schedule a vet appointment. Bring a urine sample if possible (your vet can provide a collection kit).
- 2Urinalysis and urine culture identify the bacteria and guide antibiotic choice.
- 3Complete the full antibiotic course — typically 7-14 days.
- 4Increase water intake: add water to wet food, use a pet fountain, or switch from dry to wet food.
- 5Recheck urine 7-10 days after finishing antibiotics to confirm resolution.
Dental Cleaning
$200-800For fishy breath transferring to coat — requires anesthesia.
- 1Schedule a veterinary dental exam — your vet will grade the dental disease and recommend cleaning.
- 2Professional cleaning under anesthesia removes tartar, polishes teeth, and allows extraction of severely affected teeth.
- 3Follow with home dental care: daily toothbrushing with cat-safe toothpaste, dental treats, or water additives.
- 4Dental cleanings are recommended every 1-3 years depending on the cat's dental disease progression.
- 5Dry food does not effectively clean teeth — this is a myth. Professional cleaning is necessary.
Change Diet
$0-20/month moreFor mild fishy smell with no other symptoms.
- 1Switch to a non-fish protein source — chicken, turkey, duck, or rabbit-based food.
- 2Transition gradually over 7-10 days to avoid digestive upset: mix 25% new food with 75% old, increasing the ratio over the week.
- 3If the fishy smell resolves after the diet change, diet was likely the cause.
- 4If the smell persists after 2 weeks on a new diet, pursue veterinary evaluation.
- 5Note: fish-based diets are not ideal as a primary diet long-term — they're nutritionally imbalanced for cats when fed exclusively.
When to Call a Professional
Intact female cat with foul discharge, lethargy, or swollen abdomen — possible pyometra; this is an emergency, go to a vet immediately.
Male cat straining to urinate or producing no urine — urinary blockage; life-threatening emergency, go to emergency vet immediately.
Fishy smell with anal gland area swelling or redness — infected anal gland abscess; requires prompt vet treatment.
Fishy smell with significant weight loss — possible internal disease including kidney disease; vet evaluation needed.
How to Prevent It
Annual vet checkups including dental assessment — catches UTIs and dental disease early.
Spay female cats — eliminates pyometra risk entirely.
Vary protein sources in diet rather than feeding exclusively fish-based food.
Encourage water intake with wet food, fountains, and multiple water bowls — reduces UTI risk.
Maintain healthy stool consistency with appropriate diet — firm stools naturally express anal glands.
The Anal Gland Mystery: Why Cats Sometimes Suddenly Smell Fishy
Many cat owners are caught off guard by a sudden strong fishy odor from an otherwise clean cat. The most likely explanation is anal gland leakage triggered by stress — a car ride, a vet visit, a thunderstorm, or a new pet can cause a cat to spontaneously express their anal glands, depositing the fishy secretion on their fur or wherever they're sitting.
This is a normal if unpleasant behavior — cats and dogs use anal gland secretions for scent marking. The smell is temporary and will fade from the fur within hours. If it happens repeatedly without obvious stress triggers, or if the cat is scooting or licking excessively, the glands may be impacted and need manual expression by a vet or groomer.
Frequently Asked Questions
Occasional mild fishy smell from a stressed cat expressing its anal glands is normal. Persistent fishy smell, strong fishy smell, or smell combined with other symptoms (scooting, licking, straining to urinate) is not normal and warrants a vet visit.
Sudden fishy smell is almost always anal gland expression triggered by stress or fear. Check if something stressful happened — travel, loud noise, new animal, vet visit. The smell fades within hours. If it recurs frequently or the cat is uncomfortable, have the anal glands checked.
Technically yes, but it's not recommended for inexperienced owners. Incorrect technique can push infected material deeper or rupture the gland. Have your vet do it first and show you how, especially if your cat has recurring issues. Groomers also offer this service.
Some fishy smell after litter box use is normal, especially in cats eating fish-based food. The smell should dissipate quickly. If the post-litter-box smell is especially strong, foul, or fishy-putrid rather than just normal waste smell, anal glands or a UTI may be contributing.