Many years ago when Frontline came out I used it on my toy poodles and in 24 hours there were no more signs of fleas. My Sis-in-law had them so bad they would crawl on her legs when she was in the basement doing laundry. She got some and put on her three or so dogs and they were gone within 24 hours too.
My cats and dogs, several, have never had a flea again. No way would I ever use bombs, dips or any sprays.