Fasten the Comfort Zone Cat Calming Pheromone Collar snugly with no more than two fingers width between your cat’s neck and the collar. The flexible design and breakaway feature ensures your cat won't become entangled. You may notice a white powder-like residue, called bloom, on your pouched collar, which means the pheromones are working and diffusing from the collar. Replace it every 30 days for continuous stress relief because a calm cat is a happy cat. Veterinarian recommended. For adult cats only.