Many animals obtain information about others from scent marks left in the environment, including urine. Because these marks remain after the sender has left, they allow animals to communicate across space and time. But odor molecules evaporate, degrade, and change after release. How, then, can a scent mark continue to convey reliable information about who left it?
An international research team from Japan, Germany, and Spain, led by Iwate University, has identified a candidate chemical system that may help domestic cats maintain stable individual information in urine odor. Combining behavioral experiments with chemical analyses, the researchers discovered 13 branched-chain fatty acids (BFAs) whose combinations and relative proportions differed among cats but remained relatively stable within the same individual. Cats could also discriminate between donor-specific BFA compositions when other urinary lipid components were experimentally controlled. The findings suggest that BFAs are strong candidates for carrying durable individual information—a chemical “calling card”—in cat urine. The study will be published in Current Biology .
The researchers first confirmed that cats can distinguish urine odors from different individuals. When the same urine was presented repeatedly, cats gradually spent less time sniffing it, but sniffing increased again when urine from another cat was introduced. Reduced responses to previously encountered urine odors could still be observed after intervals of months, suggesting long-term memory of urine scents.
The team then focused on the flehmen response, the distinctive open-mouthed expression familiar to many cat owners. Cats showed flehmen more frequently toward unfamiliar urine than toward their own urine, and the response decreased with repeated presentation of the same urine but increased again when urine from another individual was introduced. “After confirming that cats can distinguish individual urine odors, we used the flehmen response as a clue to identify urinary molecules that may contribute to individual scent recognition,” said Professor Masao Miyazaki of Iwate University, who led the research project.
This behavior-guided approach led to a urinary lipid fraction containing unusual BFAs. The researchers identified 13 BFAs and, based on their literature survey, found no previous reports of the same compounds in mammalian excretions or secretions. The BFA profile—the combination and relative abundance of different BFAs—varied markedly among cats but remained comparatively stable within individuals across different collection dates. Related cats tended to have more similar profiles, although individual differences were maintained even within families. BFAs were also relatively persistent. Unlike many volatile urinary odorants that change rapidly after deposition, these semi-volatile compounds evaporate more slowly. In urine-soaked samples kept at 25°C, individual-specific BFA profiles remained comparatively stable for at least 24 hours.
Crucially, the researchers showed that cats themselves could detect these differences. When other urinary lipid components were controlled and only the donor-derived BFA-containing fraction was changed, cats that had habituated to the original sample increased their sniffing. This showed that cats can detect differences in individual-specific BFA composition.
The study then revealed an unexpected connection with the kidney. BFAs were detected in the kidney but not in the other tissues examined, and BFA-containing lipids were found among neutral lipids stored in lipid droplets in the renal cortex. Intriguingly, abundant lipid droplets in cat kidneys have been known for more than 100 years, yet their biological role has remained unclear. The findings raise the possibility that these droplets act as a reservoir for BFA-containing lipids, potentially buffering short-term fluctuations caused by diet or physiological condition and helping maintain an individual-specific chemical profile in urine.
“Lipid droplets in the cat kidney have been known for more than a century, but why cats have so many of them has remained a mystery,” Miyazaki said. “Our findings suggest that one of their functions may be to support a stable chemical signature in urine. How BFAs stored in renal lipids are ultimately released into urine is an important question for future research.”
The team also examined other members of the cat family. BFA-related urinary compounds and renal lipid droplets were found in several felid species, including lions, tigers, leopards, jaguars, lynxes, and the Iriomote cat. Their BFA profiles and the amount and distribution of renal lipid droplets differed among species. BFA profiles also differed between the Iriomote cat and the Tsushima leopard cat, two geographically isolated forms of the leopard cat in Japan. These findings suggest that BFA-related chemical and physiological traits may be widespread across Felidae but have diversified during felid evolution. Whether wild felids actually use BFAs for individual recognition remains to be tested.
The significance of the study goes beyond the discovery of unusual fatty acids in cat urine. It addresses a fundamental question in animal chemical communication: how can an odor that changes over time continue to convey stable information about individual identity?
In mice, stable individual information in urine is known to involve major urinary proteins. Such a protein-based system has not been established in many other mammals. The present study suggests a different strategy in cats: combinations of semi-volatile lipid-derived molecules, potentially supported by a reservoir in the kidney, may help maintain chemical individuality over time.
Although the study is basic research and does not immediately lead to a product or technology, it opens several possible directions. Understanding BFAs could eventually contribute to approaches for controlling cat urine odor. Studying physiological lipid storage in the cat kidney may also provide clues to why lipid accumulation can be normal in some contexts but associated with disease in others. Finally, if BFA profiles can reliably identify the same individual across repeated samples, urine left in the environment could potentially provide a non-invasive tool for monitoring rare wild felids and supporting conservation.
Current Biology
Experimental study
Animals
Signatures of branched-chain fatty acids derived from a kidney reservoir confer stable chemical individuality on domestic cats
19-Aug-2026
We have no competing interest.