Common Causes (Ranked by Likelihood)
CKD is the most common serious disease in cats over 10 years old, affecting an estimated 30-40% of senior cats. As kidney function declines, the kidneys lose the ability to filter urea efficiently from the blood. Urea accumulates (uremia), and the body attempts to excrete it through alternative routes — skin, saliva, and breath. Bacteria on the skin and in the mouth convert this urea to ammonia via urease enzymes, creating the characteristic ammonia smell from the cat's coat and breath. The stronger the ammonia smell, generally the more advanced the kidney disease.
An inadequately cleaned litter box produces high concentrations of ammonia as urea in deposited urine is converted by bacteria. A cat that spends time in or near an ammonia-rich litter box may absorb ammonia onto its coat — particularly long-haired cats and those that sit or roll near the litter area. This is a hygiene issue rather than a medical one, but the result is a cat that smells of ammonia. The distinguishing feature is that the smell is concentrated on the fur surface and dissipates after the cat is cleaned, unlike CKD where ammonia emanates from the skin itself.
A UTI or feline idiopathic cystitis (bladder inflammation without infection) causes the cat to urinate more frequently, sometimes in unusual amounts and locations. Bacterial UTIs involve urease-producing bacteria that convert urea to ammonia in the bladder and urethra, making the urine itself more ammonia-rich. The cat then spreads this ammonia-rich urine on its fur during grooming of the genital area. Additionally, UTIs cause excessive licking of the genital area, spreading urine onto the fur.
Cats are obligate carnivores and require high protein in their diet, but exceptionally high-protein diets (particularly raw protein diets or very high-protein supplements) increase urea production. More dietary protein means more amino acid catabolism, more ammonia in the liver, and more urea excreted. This increases the ammonia potential in urine — which then saturates the litter box more rapidly and can transfer to fur during grooming. This is rarely the primary cause of strong ammonia smell but can amplify other factors.
How to Fix It
Get Kidney Function Tested
$100-300Essential for any older cat with ammonia odor — CKD is treatable when caught early.
- 1Book a vet visit for senior bloodwork: BUN (blood urea nitrogen), creatinine, and SDMA (symmetric dimethylarginine — detects early CKD before other markers change).
- 2A urine specific gravity test is also important — CKD cats produce dilute urine. Low specific gravity with elevated BUN/creatinine confirms CKD.
- 3CKD is staged 1-4 (IRIS staging system). Early stages (1-2) are managed very effectively with diet changes and supportive care. Cats can live well for years with managed CKD.
- 4A kidney-specific diet (Royal Canin Renal, Hill's k/d) reduces the protein load the kidneys must filter and is the primary medical management for CKD.
- 5Subcutaneous fluids administered at home are a key CKD management tool for more advanced cases — your vet will show you how.
Improve Litter Box Hygiene
$0-30For litter box-related ammonia smell saturating the cat's coat.
- 1Scoop twice daily and completely change the litter every 1-2 weeks — ammonia builds up rapidly in used litter.
- 2Use an unscented, high-absorption clumping litter — clumping litters remove urine more effectively than non-clumping, reducing ammonia buildup.
- 3Wash the litter box itself monthly with hot water and unscented dish soap. Ammonia embeds in plastic litter box surfaces over time.
- 4Add baking soda to the bottom of the box before adding litter — neutralizes ammonia.
- 5Consider a larger litter box that allows the cat to eliminate without having to stand in previously soiled areas.
Address UTI/Cystitis Medically
$100-300For male cats especially — urinary issues can become life-threatening blockages.
- 1A vet urinalysis confirms UTI (bacteria present) vs. feline idiopathic cystitis (FIC, inflammation without bacteria — the majority of feline lower urinary tract disease).
- 2UTIs are treated with antibiotics; FIC is treated with stress reduction, dietary changes, increased water intake, and sometimes pain relief.
- 3CRITICAL for male cats: Straining to urinate with no output is a urinary blockage — this is a life-threatening emergency requiring immediate vet care.
- 4Feed wet food or add water to food — hydration significantly reduces urinary crystal formation and bladder inflammation.
- 5Hill's c/d or Royal Canin Urinary S/O diets help prevent recurrent urinary issues.
When to Call a Professional
Male cat straining to urinate with little or no output — urinary blockage; this is a life-threatening emergency; go to an emergency vet immediately.
Ammonia smell with severe weight loss, vomiting, or not eating — advanced CKD or other serious illness; vet within 24 hours.
Ammonia smell with mouth ulcers or bad breath that smells of ammonia — uremic stomatitis from advanced CKD; needs medical management.
Any cat over 10 with new or worsening ammonia odor — senior bloodwork is essential.
How to Prevent It
Annual vet bloodwork for all cats over 7, twice yearly for cats over 10 — catches CKD before ammonia odor develops.
Feed wet food — increases fluid intake and supports kidney health.
Maintain a water fountain — cats drink more from moving water, supporting kidney function.
Scoop litter twice daily — prevents ammonia accumulation in the box and on the cat.
Maintain a healthy weight — obesity stresses kidneys.
Why Cat Urine Turns to Ammonia (And Why It Matters)
Urea in cat urine is converted to ammonia by bacterial urease enzymes — this is a universal process that happens in any urine left at room temperature. Cat urine converts to ammonia faster than human urine for two reasons: cats produce more concentrated urine (their kidneys are evolutionarily adapted for efficiency in low-water desert environments), and cat urine contains higher concentrations of felinine, a sulfur amino acid that also degrades to volatile odor compounds.
When a cat has kidney disease, the ammonia smell shifts from being primarily a litter box problem to a body problem — urea accumulates in the blood because the kidneys aren't filtering it efficiently, and this blood urea is then excreted through the skin (via sweat — cats do have some sweat glands) and through the mucous membranes of the mouth. Skin bacteria and oral bacteria convert this surface urea to ammonia, creating the characteristic 'kidney breath' and body ammonia smell.
Early CKD is entirely manageable. The SDMA blood test can detect kidney function decline before 75% of kidney capacity is lost — far earlier than the traditional creatinine test. Annual senior bloodwork including SDMA in cats over 7 is the most effective tool for catching CKD early when intervention is most effective.
Frequently Asked Questions
Ammonia breath in a cat is called uremic fetor and is a classic sign of kidney disease. The kidneys are not efficiently clearing urea from the blood; it accumulates and is converted to ammonia by oral bacteria. It can also occur with severe UTI. Any cat with ammonia-smelling breath should have bloodwork done — kidney values and a urinalysis are the starting point.
Yes — clumping litters remove urine more completely than non-clumping, dramatically reducing ammonia buildup. Activated charcoal litters absorb ammonia directly. Heavily scented litters mask rather than eliminate ammonia. The biggest factor though is cleaning frequency — even the best litter becomes a high-ammonia environment if not scooped at least once daily.
CKD develops slowly over months to years. The ammonia smell from the body typically appears in Stage 2-3 of CKD (IRIS staging) when kidney function has declined significantly. By the time ammonia odor is noticeable, meaningful intervention is still possible — a kidney diet alone can slow progression substantially. Don't wait on bloodwork if you notice the smell.
Kidney disease in young cats is much less common (though not impossible — some cats have congenital kidney abnormalities). In a young cat, litter box hygiene or a UTI are more likely causes. A UTI can produce strong ammonia in the urine that transfers to fur during grooming. A vet visit with urinalysis is the right first step regardless of age.