Advantage kills fleas fast. Advantage kills 98% of fleas within 12 hours and continues to work for up to one month per application. It also breaks the flea life cycle by killing flea larvae. Advantage can be used on kittens 8 weeks old and on puppies as young as 7 weeks old. Also, it is safe for use on pregnant and nursing cats and dogs. Advantage is water-resistant, so it kills fleas even after shampooing and exposure to rain.