Pheromone Diffuser Plug-ins (plugs only, no diffusers) to Reduce Cat Fighting, Spraying & Scratching Comfort Zone Calming Diffusers are vet recommended. Replace refills every 30 days and the diffuser unit every 12 months. Cats are, by nature, territorial and rely on pheromones to mark an area or object as familiar. Comfort Zone Refills are used with our diffusers to continuously release odorless, drug-free vapors that mimic cat pheromones and signal safety. When cats feel safe, behaviors like scratching and urine marking are reduced. When used consistently, most cats showed improved behavior after 2 weeks. Just plug the pheromone diffuser upright into an unobstructed outlet, away from drafts or windows in the areas and rooms where your cats spend the most time. In larger homes, consider putting a plug in diffuser on every floor. Multiple diffusers may be needed in homes with vaulted ceilings and open floor plans.