A study led by Iwate University in Japan, with researchers from Germany and Spain, has identified 13 unique branched-chain fatty acids in feline urine. These molecules form a distinct chemical signature for each cat, with the combination and proportions varying between individuals but staying relatively consistent for the same animal. The research, published on August 19, 2026, in the journal Current Biology, was led by Professor Masao Miyazaki. The study suggests these molecules originate from the kidneys, an organ that has fascinated biologists for over a century without a clear understanding of its role in such chemical signaling. Each cat's urinary signature is composed of these 13 fatty acids, allowing them to distinguish one another. Cats use a behavior known as the flehmen response, in which they open their mouths slightly, to detect and interpret these chemical signatures. Researchers used this behavior to guide their experiments, confirming that cats can distinguish the urine of different individuals. They isolated the lipid fraction of the urine that seemed to carry this individual information. Chemical analysis revealed the 13 branched-chain fatty acids, which had not previously been identified in the excretions or secretions of any mammal. These molecules evaporate more slowly than typical urinary odors, maintaining their stability for at least 24 hours at 25 degrees Celsius. This slow evaporation allows them to carry reliable information long after the urine has been deposited. Behavioral experiments confirmed that cats could detect changes in the fatty acid mixture when researchers altered only this fraction, keeping other lipids unchanged. This suggests that cats can indeed read and interpret this chemical information. Related cats showed similar fatty acid profiles, but individual differences remained even within families. For example, two kittens from the same litter would have a similar "family" scent but not identical chemical signatures. The fatty acids were found in the kidneys but not in other tissues examined. The lipids containing these fatty acids were identified among the neutral lipids stored in lipid droplets in the renal cortex. These droplets have been known for over a century, but their biological function had never been understood. Miyazaki proposes that these droplets might act as a reservoir, helping to buffer short-term changes caused by diet or physiological conditions and maintaining each cat's unique chemical profile. The exact mechanism by which these fatty acids end up in the urine remains unclear and is a key area for future research. This phenomenon is not limited to domestic cats. Similar compounds have been found in the urine of other big cats, including lions, tigers, leopards, jaguars, lynxes, and the Iriomote cat. This widespread presence in the feline family suggests that the chemical system has evolved over time, rather than emerging only in domestic cats. In contrast, mice use major urinary proteins for individual identification, not lipids. This indicates that cats have evolved a different chemical pathway to mark their presence. A deeper understanding of these urine compounds could lead to better ways of controlling cat odor and enable non-invasive monitoring of rare wild cats by analyzing the traces they leave behind.