No, Seresto does not kill fleas immediately. Seresto works slowly and effectively to kill fleas over time through the use of two active ingredients—imidacloprid and flumethrin. These two ingredients are slowly released from the collar in low doses and then spread throughout your pet’s fur when they move around or groom themselves, which is then absorbed into their skin where it begins to work to kill any existing fleas as well as prevent new ones. The goal is to treat fleas before they become a bigger problem and can cause discomfort for your pet, which can take up to 48 hours with this product depending on your pets lifestyle. It may take up to a week for full protection against new infestations.
While Seresto does not kill fleas immediately after application, its active ingredients will eventually spread through your pet’s coat and skin for up to 8 months of long-lasting protection against fleas and ticks.