I work as a veterinary assistant and have talked with representatives for both Frontline and Advantage. Both products work in a similar fashion; they are topical oils that are applied on the back of the neck, the oil then mixes with natural body oil and spreads all over the skin of the animal. As the animal sheds skin cells, the topical oil is also shed. Therefore, the animal thoroughly treats the areas around the house most commonly infested with fleas, the areas where the animal spends the most time. Incidentally, the whole house gets treated, at least lightly, as the animal sheds skin cells all over the house. The active ingredient in Advantage is a pesticide which is used on fruits and vegetables intended for human consumption, so it is pretty safe. Frontline uses a pesticide which is equally as safe. We very rarely have to suggest the use of other pesticides, such as sprays, except in cases of extremely severe infestation. Erica Snoball, the dog Ripley, Max, and Jinx, the kitties Fitz, Honey, and Buster, the ferrets [Posted in FML issue 3543]