What I normally do is give it to them at night and the next day give them a good bath, I have an expensive shampoo from the vet called Duoxo for really bad irritated skin and they are good to go for a month. Its time for mine to get their monthly flea meds now. The medicine starts killing the fleas within 30 minutes, so I would bet if you gave them a nice bath with something soothing like an oatmeal shampoo they will be in heaven!