Soap works to kill fleas in two ways. First, it will wash away the waxy coating on the flea. This leaves the pest vulnerable to injury, dehydration and attack by other parasites that are the enemy of the flea.
Soap can also work to clog up the flea’s breathing tubes. Fleas do not have lungs but have simple tubes that go straight into the blood system. Simple soap can plug them up and cause them to suffocate.
If you want to kill fleas with soap, you don’t need to use a fancy flea shampoo. Simple soap will work just fine. The typical flea dip found at your local pet store is made mostly of soap anyway.
A product such as Dawn dish soap will work to kill fleas. If you want to use something very gentle on your pet you can use baby shampoo. Mix this with some botanically based essential oils and the oil will also work as a repellant to keep fleas off of your pet in the future.
When washing your pet for fleas, be sure to wet the head first. When your pet gets wet, the fleas will automatically run for the head. They can then hide in ears, eyes and nostrils. This will make it much harder to kill the fleas and of course be very uncomfortable for your pet.
Wetting the head will cause the fleas to flee to the body and then you can attack them with your soap and oil combination.