Cat urine holds an individual chemical signature in 13 slow-evaporating fatty acids

The team worked backwards from a facial expression. Cats pull the open-mouthed flehmen face more often at unfamiliar urine than at their own, and the response fades as the same sample is offered again and rises when a new one appears ^[6]. "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 ^[7]. Guided by that behaviour, the researchers narrowed the search to a lipid fraction of the urine containing unusual branched-chain fatty acids ^[16].

The test that carries the identity claim came next. Cats detected differences between BFA profiles when the researchers controlled for the other lipids in the urine ^[11]. Relatedness mattered without erasing individuality: related cats had more similar patterns, and each animal still had its own distinguishable profile within a family ^[10]. On the authors' reading of the existing literature, these particular BFAs have not been reported before in mammalian excretions or secretions ^[3].

Durability is the part of the story the chemistry is meant to explain. BFAs are semi-volatile and evaporate more slowly than the volatile molecules that carry the smell of fresh urine ^[8]. In urine-soaked samples held at 25 C, individual profiles stayed comparatively stable for at least 24 hours ^[9]. The behaviour runs much longer: cats still investigated a previously encountered urine odour less after gaps of months ^[5]. One day of demonstrated chemical stability against a month of remembered odour is a gap of roughly thirty-fold ^[15], and the stability test was run on stored samples at room temperature, not on weathered outdoor surfaces.

The kidney part is the thinnest link in the record supplied. Iwate University's summary says the compounds appear linked to fat droplets in the kidneys and may indicate a scent-recognition system shared across the cat family ^[13]; the release does not describe the kidney work behind that statement. The paper is due in Current Biology ^[12].

What the experiments support is narrower than the "ID card" framing in the announcement: 13 compounds whose combination and relative abundance differ between cats and stay reasonably constant within one cat across sampling dates ^[1][2], plus evidence that cats notice the difference when other lipids are held constant ^[11]. Whether that profile survives a week on a fence post is a separate measurement.