FRONTLINE Plus has 2 secret weapons: fipronil and (S)-Methoprene. Once FRONTLINE Plus is applied, this combo stores itself in the oil glands in your pet's skin. It then self-distributes continuously for 1 month to your pet's hair and skin through the hair follicles. Fleas or ticks that come in contact with your pet are dead meat. In a study, FRONTLINE Plus began killing fleas 4 hours after application.1 Another study showed that within 12 hours, Frontline Plus killed 100% of fleas. FRONTLINE Plus kills fleas and ticks through contact with your pet's haircoat. No biting necessary.