Frontline is the most common flea treatment recommended by vets. They know Frontline Spot On kills parasites fast and goes on protecting your pet. Frontline Spot On Dog works by both preventing flea and tick Frontline is also effective against biting lice and it is effective against fleas for up to 5 weeks and ticks for up to 1 month. It also controls lice within 48 hours. How does Frontline Spot-On work? Frontline Spot On acts directly on fleas, ticks and lice and not via your pet’s bloodstream. It kills fleas within 24 hours without the need for them to bite your pet. The dog flea treatment is applied externally on the back of the neck, where the active ingredient, Fipronil, quickly dissolves into the natural oils on your pet’s skin and coat. Within 24 hours it disperses over the entire body surface and also concentrates in the skin's oil glands to form a reservoir.