Your Cat Carries a Chemical Business Card, and It Is Made in the Kidneys
Cats leave a scent that says which cat left it, and it holds for at least a day. Japanese researchers have found where it comes from: fat droplets in the kidney that nobody could explain for over a century.
Anyone who has watched two cats meet knows the pause: the long, careful sniff, and then a decision. A team at Iwate University in Japan has now worked out what is actually being read in that moment, and where it is manufactured, and the answer sat unexplained in every anatomy textbook for more than a hundred years.
Cat urine carries thirteen branched-chain fatty acids in a mixture that differs from cat to cat. In the tests, cats that had grown bored of one sample started sniffing again as soon as only that fraction was swapped, which is the polite scientific way of saying they noticed a different individual had been there. The mixture holds its shape for at least twenty-four hours at room temperature.
Cookie · Editor-in-chief
So I have a business card. Made of pee. That I hand out constantly.
Nora · Adoption desk
It lasts a full day, apparently.
Cookie · Editor-in-chief
Networking.
The strange part is the factory. Those fatty acids turned up in the kidney and nowhere else the team looked, stored in lipid droplets in the renal cortex. Cat kidneys have been visibly full of these droplets since anyone first put one under a microscope, and nobody knew what they were for. "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," said Masao Miyazaki, who led the work. The droplets appear to act as a reservoir, topping the signature up so it stays recognisable whatever the cat had for dinner.
They found the same droplets, with different recipes, in lions, tigers, leopards, jaguars and lynxes. Two isolated populations of the same Japanese leopard cat came out with different signatures from each other. The team has not published how many cats were tested, and whether wild cats actually use any of this to recognise each other is still an open question.
None of which changes anything you do on a Tuesday, except perhaps how you read the sniffing. Your cat is not being rude to the visitor's trousers. It is checking the reference section.
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