Frontline Plus Flea Control Plus for Dogs And Puppies - 45-88 lbs - 3 PackFrontline breaks the parasite's life cycle, thus preventing them from laying eggs and reproducing. Frontline is applied to the back of the neck of cats and between the shoulder blades of dogs. Frontline spreads naturally on the skin surface at the hair root level, aided by body movement to provide whole body coverage. Frontline is water resistant flea medication, so it continues to kill fleas even after shampooing, swimming, rain, or exposure to