Researchers have identified 13 unusual branched-chain fatty acids in cat urine that vary across individuals and remain stable for at least 24 hours, functioning as a durable chemical “calling card” that helps preserve information about individual identity for domestic cats.
Cats rely heavily on scent to interpret their surroundings, gathering chemical traces from urine left behind long after another cat has moved on. This creates a biological puzzle because many odor molecules break down or evaporate over time. A research team spanning Japan, Germany, and Spain, led by Iwate University, set out to discover how cats solve this mystery, ultimately identifying a group of 13 unusual fatty acids that could act as a lasting chemical signature. The study is slated for publication in Current Biology.
Long-Term Memory and the Flehmen Response
Before searching for the chemical compounds themselves, the scientists tested whether cats could actually distinguish between the urine of different individuals. When presented with the same urine sample repeatedly, cats gradually lost interest and spent less time investigating it. However, introducing urine from a new cat caused their interest to spike again. Remarkably, cats continued to show reduced responses to previously encountered urine odors even after gaps lasting months, pointing toward long-term scent memories.
Researchers also monitored the flehmen response—the distinct open-mouthed expression cats make when processing certain odors. Cats displayed this behavior more frequently when smelling unfamiliar urine compared to their own scent. As the researchers repeatedly presented the same sample, the flehmen response waned, only to increase again when they introduced urine from a different cat. 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.
Thirteen Unusual Branched-Chain Fatty Acids Form Distinct Profiles
Using behavioral observations to narrow their focus, the scientists isolated a lipid fraction in urine containing unusual branched-chain fatty acids, known as BFAs. A review of existing scientific literature revealed no prior reports of these specific BFAs occurring in mammalian excretions or secretions. Rather than the simple presence of the chemicals, it was the specific pattern—the combination and relative abundance of the different fatty acids—that stood out.
Each animal maintained a BFA profile that varied considerably from other cats while remaining relatively stable when researchers sampled the same cat on different dates. Genetics also appeared to influence the profiles, as related cats generally displayed more similar BFA patterns, though each animal retained its own distinct signature.
Unlike many volatile odor chemicals that alter quickly after deposition, these BFAs are semi-volatile and evaporate at a slower rate. In urine-soaked samples stored at 25°C, the unique profiles remained comparatively stable for at least 24 hours.
To confirm that cats perceive these chemical differences, researchers controlled other lipid components in the urine while altering only the donor-derived BFA fraction. Cats accustomed to the original sample began sniffing more actively once the BFA fraction changed, confirming that they can perceive individual BFA variations.
While volatile scent traces quickly break down in the environment, the semi-volatile nature of these 13 fatty acids allows individual signatures to persist for at least a full day at 25°C, bridging the gap between fleeting odor molecules and long-term memory.
That durability connects directly to the long-term memory experiments, where cats recognized familiar scent profiles months later. While volatile compounds fade, a stable BFA fraction could provide the consistent baseline necessary to trigger those stored memories.
Genetics shapes these chemical identities—related cats share closer BFA compositions—yet every individual maintains a distinct profile even within the same family group.
Unlocking a Century-Old Cat Kidney Mystery
The investigation also uncovered an unexpected clue located in the kidneys. Researchers detected BFAs in kidney tissue, but not in any of the other tissues they examined. Furthermore, lipids containing BFAs appeared among neutral lipids stored inside droplets in the renal cortex.
These kidney lipid droplets have puzzled scientists for over a century. Although domestic cats are known to possess large numbers of them, their exact biological purpose has remained uncertain.
Persistent Questions in Feline Chemical Communication
Despite identifying the 13 BFAs and their role in individual scent recognition, the research leaves several questions unanswered. The sources do not report whether environmental factors such as diet, age, or stress alter a cat’s BFA profile over longer spans than the tested 24-hour window, nor do the sources clarify the exact biochemical pathway by which the renal cortex lipid droplets produce these specific fatty acids.
