Cats Have Been Leaving Each Other Chemical Voicemails This Whole Time

A new international study finds cats identify one another through a durable set of 13 fatty acids in their urine, and the source of that steady signature may be hiding inside a century-old kidney mystery.

Cats already run most of their social lives through scent, leaving urine marks that keep communicating long after the cat that made them has wandered off. But that raises an obvious question: most odor molecules evaporate or break down fairly quickly, so how does a cat sniffing a days-old mark still know exactly whose it was?

An international research team led by Professor Masao Miyazaki at Iwate University, working with collaborators in Germany and Spain, thinks they've found a real piece of the answer: a set of 13 unusual, slow-to-break-down fatty acids in cat urine that function like a durable chemical calling card. The mix and ratio of these compounds, known as branched-chain fatty acids, or BFAs, differs from cat to cat, but stays remarkably consistent for any individual animal over time.

Before chasing the chemistry, the team first had to confirm cats could actually tell individuals apart by scent alone. They used a classic habituation test: cats lost interest in a urine sample they'd already sniffed repeatedly, then perked right back up when a different cat's urine was introduced. That renewed interest held up even after gaps of several months, hinting that cats may hold onto scent memories of specific individuals far longer than expected.

The team also tracked the flehmen response, that open-mouthed, slightly goofy grimace cats make while processing certain smells. Cats flehmened more at unfamiliar urine than their own, the response faded with repeated exposure to the same sample, and it spiked again the moment a new cat's urine showed up.

“After confirming that cats can distinguish individual urine odours, we used the flehmen response as a clue to identify urinary molecules that may contribute to individual scent recognition,” Miyazaki said.

That trail led to a lipid fraction in the urine and, eventually, to the 13 BFAs. Each cat's particular combination and relative abundance of the compounds forms a profile that varies a lot between animals but holds steady in the same cat across different sampling dates. Related cats tend to have somewhat similar profiles, but even littermates keep their own distinguishable signature. And unlike the more volatile compounds responsible for typical urine odor, BFAs are semi-volatile, evaporating slowly enough that a distinct profile stayed measurably stable for at least 24 hours in samples held at room temperature.

To confirm cats could actually perceive those specific differences and weren't just reacting to something else in the sample, researchers held every other lipid component constant and swapped out only the BFA fraction. Cats that had grown bored of the original sample started sniffing again, evidence that the BFA pattern itself, not just “a new smell” in general, was carrying the identifying information.

The study's biggest surprise showed up somewhere researchers weren't necessarily looking: the kidney. BFAs turned up in kidney tissue but not in the other organs the team examined, tucked into fat droplets stored in the renal cortex. Those droplets have puzzled scientists for more than a hundred years. Cats are known to carry an unusually large number of them, but nobody has pinned down what they're actually for.

“Our findings suggest that one of their functions may be to support a stable chemical signature in urine,” Miyazaki said, framing the droplets as a possible storage reservoir that buffers short-term shifts in diet or physiology, keeping a cat's chemical “name tag” steady even as everything else about its body fluctuates day to day. “How BFAs stored in renal lipids are ultimately released into urine is an important question for future research.”

The pattern isn't unique to house cats, either. BFA-related compounds and the same kind of renal lipid droplets turned up in urine and kidney tissue across a wide range of felid species, including lions, tigers, leopards, jaguars, lynxes, and the Iriomote cat, suggesting a chemical ID system that may run across the whole cat family rather than being a domestic-cat quirk.

For clinicians, this is early-stage basic science rather than anything ready for the exam room, but it's the kind of finding worth filing away. A better understanding of how cats encode and recognize individual identity could eventually feed into conversations about inter-cat aggression, marking behavior, and stress in multi-cat households, all common reasons owners end up in a feline behavior consult in the first place. The study is set to be published in Current Biology.

Source: Research led by Prof. Masao Miyazaki, Iwate University, in collaboration with institutions in Germany and Spain, forthcoming in Current Biology.