Looking for answer that is scientific in nature and not just an opinion.
When using dial (on my cat) it helps kill the fleas, sometimes better than even cheap flea-shampoos do. But like those cheap shampoos, does it or does it not kill all 4 stages in a flea's life cycle (ex. some shampoos don't kill eggs)??
Question 2 is using dial first before a store-bought, flea-shampoos does it cover say the eggs with a layer that the flea-shampoo doesn't penetrate to kill the egg??
Dish soap, bar soap, liquid soap, shampoo (for humans) is a no-no for cat's (or dogs). Cats skin is a significantly different Ph than human skin and using these products can cause irritation, itching, allergies, etc. Additionally, when they groom themselves, they can ingest chemical traces that may cause other issues in the future.
For good flea control, there are many, many methods and products. Do a search here on the site and you will find many answers for flea control.
I use Comfortis on my cat and dog and have been extremely pleased. They both have no reaction to the treatment.
As you are are looking for an answer that is scientific in nature. I have to start by saying you maybe working under a false impression. There is a well researched answer at Can dish soap really be used to kill ticks and fleas? that conflicts with the popular belief that fleas are easy to drown, soap can help wash fleas off, but it does not drown them. There is a second answer at the same question, that indicates some dish soap that MAY kill fleas can be harmful to cats.
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