In 1997, Bayer said not to bathe dogs after applying Advantage, as it may wash off. This gave Merial a huge marketing message, that FrontLine didn’t wash off easily.
Bayer soon reversed the bathing information they gave to veterinary practices. Their product testing indicated that the product was indeed less effective after baths, but field data after several million doses had been purchased and applied indicated that most pet owners did not wash their dogs as thoroughly as did the testing teams. The official word to us was that baths were OK.
In general, if you are applying something that costs $12–20, why do you want to wash your dog right away? Bathe first, wait two days for the skin to replenish its oils (used for the products to travel over the whole body), then apply the topical product.
This is only part of why we recommend prescription oral flea products.