Cats leave urine marks around their territory, and other cats sniff them with great care. A team led by Masao Miyazaki at Iwate University in Japan, working with researchers in Germany and Spain, asked how a mark can keep saying who left it when smell molecules evaporate and break down after they land. Their answer, published in Current Biology on 19 August 2026, is a set of 13 branched-chain fatty acids.
They started from behavior. A cat that sniffed the same urine sample again and again lost interest, then sniffed more when a different cat's urine was offered. Cats also made the flehmen face, a slightly open mouth that sends scent to an organ in the roof of the mouth, more often at unfamiliar urine than at their own. Using that face as a guide, the team narrowed the urine down to a fatty fraction and found the 13 compounds. In the scientific literature they found no earlier report of the same compounds in what any mammal excretes or secretes.
Each cat had its own combination and proportions of the 13, and the profile of a single cat stayed much the same. In urine left at 25°C (77°F), the individual profiles held comparatively steady for at least 24 hours. Cats could tell two donors apart even when the rest of the urine fats were rebuilt to match, so the difference came from these compounds. Cats also still responded less to a urine smell they had met before after gaps of months.
The compounds lead back to the kidney. Cat kidneys have been known for more than 100 years to hold many fat droplets in their outer layer, the cortex, without anyone knowing why. The team found the fatty acids stored in fats inside those droplets and suggests they act as a reservoir that smooths out short changes from diet or health, so the tag stays readable.
Lions, tigers, leopards, jaguars, lynxes and the Iriomote cat showed related compounds and kidney droplets too, with differences between species. Whether wild cats actually use them to recognize each other has not been tested yet, and this is one study: the authors call the fatty acids strong candidates for the signature, not the final word.
