Most of the soaps in the market are actually detergent, i.e. the material used are Sodium Lauryl Sulfate ( SLS), Sodium Laureth Sulfate (SLES) which are the base materials for making detergent , SLS functions as a surfactant ( surface active agent) or cleansing agent. Because of its cleansing effect, all the fats that functioned to protect the skin are also being dissolved, thus causing skin dryness and skin irritation.
Commercial bath soaps generally contained a lot of petroleum derivatives ingredients which are harmful and damaging to the skin.