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Rare fatty acids in kidney fat droplets may help cats recognize who left a scent.
A cat that sprays a wall may be doing more than declaring ownership (and stinking up the whole place). It may be leaving behind the chemical equivalent of a name tag — one assembled from rare fatty acids and stored, before release, in an organ not usually associated with communication: the kidney.
In a new study, researchers identified 13 branched-chain fatty acids, or BFAs, whose relative proportions differed from cat to cat yet remained unusually consistent within the same animal. Cats could distinguish those donor-specific mixtures even when researchers controlled the rest of the urine’s lipid chemistry. The team traced the compounds to fat-rich droplets in the outer part of the kidney, suggesting that the organ acts as a reservoir that helps keep each cat’s chemical signature steady.
This sounds like a clever solution that feline biology found to a basic problem in animal communication: smells change. Molecules evaporate, diets shift and bodies change, yet a territorial scent mark is useful only if another animal can still tell who left it. Cats may solve that problem with a relatively durable layer of small molecules backed by a biological storage system.
The team collected urine from 44 domestic cats and used 27 cats in behavioral experiments; several of the core recognition tests involved the same seven male subjects. When cats repeatedly encountered urine from the same donors, they gradually spent less time investigating it. Introduce urine from a new cat, and their interest returned. In another experiment, cats retained familiarity with a previously encountered urine odor over intervals of months.
The researchers watched for the flehmen response — the open-mouthed, slightly vacant expression cat owners sometimes call a “stink face.” The behavior helps funnel scent molecules toward the vomeronasal organ, which cats use to analyze certain chemical signals. The cats performed it more often when smelling urine from an unfamiliar cat than when smelling their own.
“I found it surprising that an innate behavior could be so strongly influenced by familiarity and learning, rather than being a simple fixed response to a single pheromone,” Masao Miyazaki, a biomolecular scientist at Iwate University and a study co-author, told Live Science.
The team then separated urine into chemical fractions and let cats investigate them. One fraction repeatedly triggered flehmen. Chemical analysis revealed an unusual group of BFAs, several of which, the authors wrote, had not previously been reported in mammalian excretions or secretions.
More importantly, the mixtures looked like individual fingerprints. Related cats tended to resemble one another, but each retained a distinctive profile. And when urine-soaked pads sat at 25 degrees Celsius, those profiles changed little over 24 hours, even as the more volatile components of urine drifted.
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The new result builds directly on an earlier puzzle. A 2019 study of domestic cat urine found that cats could distinguish individuals by smell, but that hundreds of volatile compounds changed strongly as urine aged. The authors proposed that some unknown, more stable chemicals might carry identity.
The BFAs now fit that description unusually well. When researchers created a common “background” of urine lipids and swapped in a BFA-rich fraction from a different donor, cats started sniffing again. That indicates they could detect the change in BFA composition itself, rather than simply reacting to some other difference between two urine samples.
Still, the researchers have not cracked a complete feline name code. A synthetic mixture containing six representative BFAs was less effective by itself than the natural BFA-rich fraction. The cats may read the full mixture, a subset of it or one or two especially informative compounds. The receptors and brain circuits involved also remain unknown.
There is a useful precedent in mice. An old 2001 Nature study showed that wild house mice use highly variable major urinary proteins, or MUPs, as part of individual recognition. Cats appear to have arrived at a different molecular solution: semi-volatile fatty acids rather than long-lived proteins.
The most unexpected result came from the kidney. BFAs appeared prominently in kidney extracts but not in serum, liver or other tissues the researchers examined. They were concentrated in triacylglycerols — storage fats — inside lipid droplets packed into cells of the renal cortex. Those kidney BFA profiles also differed from cat to cat.
“Connecting this unusual [kidney] feature with urinary chemical signals was completely unexpected,” Miyazaki told Science.
Similar BFA-related chemistry turned up across the cat family, including lions, tigers, leopards, jaguars, servals, Iberian lynxes and leopard cats, although the mixtures and kidney fat patterns varied considerably among species. The researchers remind us that they tested behavioral recognition only in domestic cats, so they cannot yet say that wild felids use BFAs in the same way.
But what does all this mean for feline kidney health? A separate 2026 lipidomics study reported that felid kidneys contain more intracellular lipid than dog kidneys and proposed that unusual renal fats could be involved in chronic kidney disease. If kidney lipid droplets serve a normal communication function, researchers will now have to understand when that storage system is useful and when, if ever, it becomes harmful.
“We now want to understand how these lipid droplets are formed, maintained, mobilized and linked to secretion into urine,” Miyazaki told Live Science. “We are also very interested in whether disruption of these processes contributes to chronic kidney disease in cats.”
The findings were reported in the journal Current Biology.

Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines. He has a B.Sc in mechanical engineering and an M.Sc in renewable energy systems.
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© 2007-2025 ZME Science – Not exactly rocket science. All Rights Reserved.