Mice display different social behaviours towards juveniles and adults, but the underlying mechanisms are unknown. The authors identified a pheromone, ESP22, in juvenile mouse tears. Adult males demonstrated increased sexual behaviour towards juveniles lacking ESP22, and this behaviour was attenuated when the juveniles were 'painted' with ESP22. ESP22 activated receptors in the vomeronasal organ (VNO) and adults lacking TRPC2 (which is essential for VNO signalling) exhibited increased sexual behaviour towards juveniles, confirming the role of the VNO in mediating the effects of EPS22.