I had a horrendous flea infestation 21.5 years ago where I couldn’t bring my newborn home. Had to go to mom’s and “bomb” the house.
Then a co-worker told me about brewer’s yeast. give 1 tablet for every 10 pounds of dog once a day. You can get them on amazon for $8.88 for 1000 pills. I had 3 dogs and 3 cats (simultaneously) and have just added a puppy. We have NEVER had fleas in 21.5 years. Never. I live in the Northeast and give the pills every day from March 1 until Nov 1 (or first frost). HIGHLY HIGHLY recommend this. All 6 of the animals love them – they think they’re treats.
Brought a rescue puppy home on Saturday–guess what he brought with him? First fleas in 21.5 years. So far, only he has them. You can bathe animals in blue Dawn dish detergent (this is what rescue workers bathe animals in that have been caught in oil slicks). It kills the fleas on contact. Make sure it’s Dawn and not Palmolive or other brand; only Dawn kills them on contact (that I’ve found). I don’t want to put spot treatments on this puppy, so he’s been enjoying his new “treats” every time he goes outside and comes back in. I’ve put the other animals back on the treatment early this year.
There might be no scientific proof, but over the 11 animals I’ve had in the past 21.5 years, I swear by brewer’s yeast. Matter of fact, just ordered 2 bottles.