Thirteen Fatty Acids Form a Stable Identity Code in Cat Urine, Study Finds

Domestic cats carry a durable chemical signature built from 13 branched-chain fatty acids (BFAs) in their urine, and that profile stays distinct enough to identify an individual for at least 24 hours after the mark is laid down, according to a study published in Current Biology on September 20, 2026.

The work, led by Professor Masao Miyazaki of Iwate University in Japan with collaborators in Germany and Spain, reframes a long-standing question: how scent marks continue to convey identity even as volatile odor compounds evaporate and degrade within minutes of deposition. The answer in cats appears to be lipid-based rather than protein-based, setting felines apart from mice, where major urinary proteins perform a similar identity-preserving role.

What did the experiments actually show?

Researchers first confirmed that cats can tell urine from different individuals apart. When presented repeatedly with the same sample, cats spent less time investigating it; introducing a new cat's urine reliably restored interest. That pattern persisted across multi-month gaps, suggesting long-term odor memory.

The team then used the flehmen response — the open-mouthed grimace cats make when sampling certain odors — as a behavioral marker. Flehmen occurred more often with unfamiliar urine and tapered with repeated exposure, a signal that cats were tracking individual-specific chemistry rather than generic odor strength.

"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," Miyazaki said.

Guided by that behavior, the researchers fractionated urine and identified 13 BFAs, a class of compounds not previously reported in mammalian excretions or secretions. Each cat carried a unique combination and ratio of these fatty acids. Profiles varied substantially between animals, held relatively steady across sampling dates, and were more similar among related cats, indicating a partial genetic influence.

Why do the profiles last?

BFAs are semi-volatile, evaporating far more slowly than the small odorants that dominate fresh urine scent. In samples held at 25 °C, the distinguishing BFA profile of an individual remained intact for at least 24 hours.

In a follow-up test, researchers swapped only the BFA-containing fraction of a urine sample while keeping other lipids constant. Cats that had habituated to the original sample resumed intensive sniffing, direct evidence that they perceive the BFA component itself rather than downstream odor cues.

What does the kidney have to do with it?

The team detected the same BFAs in feline kidney tissue but in no other organ examined, concentrated inside neutral-lipid droplets of the renal cortex. Those droplets have been documented in cats for more than a century without a clear function.

The new data suggest the droplets act as a storage reservoir that buffers day-to-day metabolic and dietary variation, helping keep the urinary BFA profile stable. "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."

Does the same chemistry exist in other cats?

BFA-related compounds and renal lipid droplets appeared in urine and kidney samples from lions, tigers, leopards, jaguars, lynxes, and the Iriomote cat. Species-specific BFA profiles and droplet distribution patterns varied, with measurable differences even between the Iriomote cat and the Tsushima leopard cat, two isolated Japanese leopard-cat populations. The authors interpret this as a shared felid system that has continued to diversify through evolution, though behavioral confirmation in wild cats is still lacking.

What changes at the exam table or in the field?

For companion-animal practice, the immediate impact is limited. The work is basic research with no diagnostic test, drug, or FDA CVM-regulated product in development. Veterinary teams can, however, use the findings to counsel clients that persistent urine marking carries identity information lasting at least a day, a fact relevant to multi-cat household introductions and to designing cleaning routines that actually remove a resident cat's signal.

For wildlife and conservation medicine, the implications are more concrete. If BFA profiling can be standardized, non-invasive urine sampling from the environment could eventually allow researchers to identify individual rare felids — Amur leopards, Iriomote cats, snow leopards — without trapping, sedation, or camera-trap dependency. Validating that approach across species is the next step.

The authors also flag a translational research angle: cats normally accumulate renal cortical lipid droplets without apparent harm, while lipid accumulation in other species signals disease. Understanding how felines handle BFA-rich lipid storage may inform comparative work on renal lipidosis and metabolic lipid handling.

What is still unknown?

The mechanism by which BFAs are mobilized from renal droplets into urine remains uncharacterized, as does whether wild felids use the same BFA-based recognition system in social or territorial contexts. Cross-species validation in controlled behavioral trials — and longitudinal urinary BFA profiling in captive populations — will determine whether the 13-fatty-acid signature becomes a practical tool for veterinarians and conservation biologists or remains a curiosity of feline biochemistry.

Study reference: Ichizawa S, Caspers J, Uenoyama R, et al. Signatures of branched-chain fatty acids derived from a kidney reservoir confer stable chemical individuality on domestic cats. Current Biology 2026;36(17):4340. DOI: 10.1016/j.cub.2026.07.045.