The pungent smell of used cat litter comes primarily from odorant molecules released as urine decomposes. Among them, we can blame ammonia for being the main cause of the foul stench. Luckily, several solutions exist to control litter box odor and preserve harmony between cats and their parents.


Most of the time, cats are beloved members of the family, but when their litter box stinks, it’s another story.


Poop reeks, but the offensive odor can be easily managed by removing feces from the litter box. However once feces are gone, the urine smell lingers.


As chemical reactions occur in the urine, volatile molecules such as ammonia are released. They are responsible for that litter box odor so unpleasant for cat owners.



Ammonia, the number-one enemy


Highly volatile, detectable by humans at very small concentrations, ammonia is the chief compound responsible for the bad smell wafting up from the cat litter. Its characteristic fishy odor is particularly offensive to pet parents.


Ammonia is created by the bacterial decomposition of urea, the primary component of urine.



A huge number of bacteria are found in a litter box. They can be brought by the cat from the environment, carried on the cat’s skin, emerge with cat feces, or be present in litter substrate.


Some of these bacteria produce an enzyme called urease that converts urea into ammonia and carbonic acid.


The amount of urea in cat urine is particularly high compared to other species like dogs and humans.




Once the cat litter has been soiled, the urea-positive bacteria quickly degrade urine, leading to the creation of a large amount of ammonia.



From felinine to sulfur compounds, this familiar “catty” odor


Another cause of the typical unpleasant smell of a cat litter box is the degradation of felinine, a pheromone specifically found in the urine of some members of the family Felidae.


In cats, the excretion of felinine starts from the age of 3 months and is higher in intact males than in castrated males and mature females.



Felinine itself has no odor. However, its degradation generates sulfur compounds – the thiols – responsible for the recognizable “catty” odor.


The degradation of felinine – the mechanisms of which are not completely known at this time – also generates pyruvic acid, which has a sour odor, as well as a small amount of ammonia. Both molecules reinforce the overall bad litter smell over time.




4 ways to manage litter odor


There are two main approaches to limit bad smells emitted from the litter box. Cat litter manufacturers can try to prevent unpleasant odors from forming, or they can develop solutions to manage the odorant compounds once they are created.



1 – Prevention of odor formation



Preventive measures are among the best approaches to counteract bad litter box smells. They can be applied in special cases when unpleasant odors form over time and when the source of the odor is known.


The most common approaches aim at stopping the urea degradation process to limit ammonia release.






  • Urease inhibitors


Manufacturers can use blockers to lock urease activity, thus avoiding formation of ammonia.


  • Antimicrobials


Urease is produced by bacteria, so including antimicrobials in the litter is another way to limit urea degradation. That helps, but when bacteria die, the urease they contain is released and continues to change urea into ammonia.


Antibacterials should thus be used in combination with other anti-odor solutions such as fragrances.



2 – Odor Elimination




Another strategy to fight unpleasant litter box smells is to act directly on the malodorous compounds.


Manufacturers can include in their products specific molecules that will react with the volatile odorants and remove them from the air before they reach the nose.





3 – Masking odors




Manufacturers can also include fragrances in litter to cover up smelly compounds. This method makes the perception of odors less offensive to owners by creating a new, more pleasant olfactive context.


The challenge is to select molecules agreeable to the owner and accepted by the cat.





4 – Suppression of odor perception




Finally, manufacturers can act on the cat owner’s olfaction system by using compounds that block olfactive receptors or olfactive signals in order to reduce the perception of offensive odors.






Litter box odor is one – if not the main – nuisance of cat ownership. It can considerably affect the bond between the animal and the owner.
Fortunately, litter manufacturers have several solutions to fight bad smells and breathe new life into the environment of cats and their parents.



– Y. H. Cottam, P. Caley, S. Wamberg, W. H. Hendriks, 2002. Feline Reference Values for Urine Composition. American Society for Nutritional Sciences. J. Nutr., 132, pp 1754S–1756S. doi : 10.1093/jn/132.6.1754S
– E. A. Hagen-Plantinga, G. Bosch, W. H. Hendriks, 2014. Felinine excretion in domestic cat breeds: a preliminary investigation. J. Anim. Physiol. Anim. Nutr., 98(3), pp 491 496. doi: 10.1111/jpn.12097
– W. H. Hendricks, S. M. Rutherfurd, K. J. Rutherfurd, 2001. Importance of sulfate, cysteine and methionine as precursors to felinine synthesis by domestic cats (Felis catus). Comp. Biochem. Physiol. C Toxicol. Pharmacol., 129(3), pp 211-216.
– W. H. Hendriks, K. J. Rutherfurd-Markwick, K. Weidgraaf, R. Hugh Morton, Q. R. Rogers, 2008. Urinary felinine excretion in intact male cats is increased by dietary cystine. Br. J. Nutr., 100(4), pp 801-809. doi: 10.1017/S0007114508945165.
– P. Kafarski,M. Talma, 2018. Recent advances in design of new urease inhibitors: A review. Journal of Advanced Research, 13, 101–112. doi: 10.1016/j.jare.2018.01.007
– M. Miyazaki, T. Yamashita, Y. Suzuki, Y. Saito, S. Soeta, H. Taira, A. Suzuki, 2006. A Major Urinary Protein of the Domestic Cat Regulates the Production of Felinine, a Putative Pheromone Precursor. Chemistry & Biology 13, 1071–1079. doi: 10.1016/j.chembiol.2006.08.013
– S. M. Rutherfurd, T. M. Kitson , A. D. Woolhouse, M. C. McGrath, W. H. Hendriks, 2007. Felinine stability in the presence of selected urine compounds, Amino Acids 32: 235–242. doi: 10.1007/s00726-006-0369-z
– Starkenmann, C., Niclass, Y., Cayeux, I., Brauchli, R., A.-C. Gagnon, 2015. Odorant volatile sulfur compounds in cat urine: occurrence of (+/−)‐3,7‐dimethyloct‐3‐sulfanyl‐6‐en‐1‐ol and its cysteine conjugate precursor, Flavour Fragr. J., 30, pages 91– 100. doi: 10.1002/ffj.3216.
– WBK & Associates Inc., 2004. Assessment Report on Ammonia for Developing Ambient Air Quality Objectives – Vol1 for Alberta Environment.
– J. Zentek, A. Schulz, 2004. Urinary Composition of Cats Is Affected by the Source of Dietary Protein J. Nutr., 134, pp 2162S–2165S. doi: 10.1093/jn/134.8.2162S


take-home points

  • The degradation of urine generates smelly compounds
  • Ammonia is the main molecule responsible for cat litter box odor
  • Prevention, elimination, masking and suppression are among the options that exist to limit odor in cat litter