Ok so i've tried frontline on my cats, didn't help much.. it worked at first but they keep getting more fleas esp the adult ones i dont understand it. They are INSIDE cats and we live on the 3rd floor. All i can t hink is they are coming from an outside source. I dont understand why they are only on the two cats and we haven't had any on us or seem them around the house. I just don't get where they keep appearing from????