I raise Yorkies and usually average having about 7 or 8 adult dogs in the house at the same time. Diatomaceous Earth works best as a prevention and maintenance treatment, in my opinion. If you have a bad infestation, you need to use an oral medicine to get rid of the fleas. And then you need to treat the environment. I have sprinkled D/Earth on my couch, my carpet, my mattress, around the doorways, the yard, and everywhere my dogs might go. You can even sprinkle it on their food to kill internal parasites. It works by cutting the shell of the fleas causing them to die from dehydration. So, if any flea eggs hatch, they die before they start biting. And since it is ground fossils, you don't have to worry about an chemical harm to anything.