A flea infestation can be a source of great suffering for your cat or your dog. Fleas can cause constant itching, pain (from biting again and again), and if swallowed, fleas can cause tapeworms. Nothing is more effective for protecting your house and your pets from flea infestation and lice than Advantage cats and dogs. Advantage kills fleas at all stages and on contact, so your cat or your dog doesn't have to get bitten in order to kill them.