The skin is protected by a thin acidic layer called the acid mantle. This layer guards the skin from infections, helps in skin renewal, gives it a glow and makes it soft and smooth. Harsh soaps damage this layer as they have a pH > 7. Continuous use of cleansers / moisturisers with unbalanced pH creates a traumatic condition for the skin which will show effects like early wrinkles, skin sagging, skin infections.
If one has used such products and not had any problems, there is no guarantee that these problems may not crop up ever. In fact the faster one switches to Sebamed further damage can be avoided.