75-80% of your flea problem isn't on the dog. I see it almost daily where I start an animal with a flea problem on prevention and they call a few weeks or a month later and say it isn't working. It takes time before the stages of the life cycle all hatch out, and feed on your dog and die, before laying more eggs. That's the whole premise with flea prevention, they have to have a blood meal to lay eggs. So when they feed on an animal with prevention, they die before laying eggs. It can take months to rid an area of fleas.
