Frontline contains Fipronil which kills 100 per cent of fleas and ticks within 24-48 hours of them contacting it. Fleas are killed before they bite! Frontline Plus has S -methoprene added in, an Insect Growth Regulator, which prevents new fleas from maturing. Both products stay on even through bathing or swimming. Apply the product once a month on the middle of the pet's back for long lasting protection.