Fleas, of course, are aggravating little insects that carry disease, frequently cause intense skin reactions and allergies in our pets, and can be extremely difficult to control. Fleas are notoriously good at becoming resistant to the pesticides we use to control them, so many of the products available are nearly useless. The trouble is that fleas have become resistant to the pesticides we've been using for the last 25 years. Luckily, we now have new pesticides that they haven't become resistant to, and in most cases are working really well. And many of these newer products also control other parasite problems well.