Cats naturally produce invisible calming messages known as pheromones. Thanks to the advanced messaging of the Patented Feline Pheromone complex, Feliway Optimum Enhanced Calming Pheromone 30 Day Cat Diffuser Refill provides feline friends with a message of enhanced calming. This holistic message helps cats feel more comfortable and secure in their home by providing reassurance as well as harmony between cats who are living together.