Dawn dish soap kills fleas on dogs. The soap damages the exoskeletons of the fleas, killing them almost instantly. It is best to use the dish soap in place of pet shampoo as part of the dog's regular bath.
To kill fleas on a dog with Dawn dish soap, prepare a regular bath for the pet. Apply several tablespoons of the soap directly to the animal's fur and work it into a lather. Rinse well. This method may take several baths to completely kill the fleas, depending on the severity of the infestation. It is not recommended for use in place of other flea-prevention methods.