That's not a stupid question at all. I asked my vet about this. The topical products go into the skin in the subcutaneous fat layer. In order for it to get there, the hair and skin should NOT be too clean so that the natural oils will allow it to move where it needs to go. The vet said to wait at least 3 days after a bath, and dont bathe for at least 3 days after the application (these guidelines are for the dog....not the owner

).