Although dishwashing soap does a fair job of cleaning a car, it contains abrasive mineral particles like powdered chalk, silica, marble, and volcanic ash. These particles do a great job cleaning dishes, but they can accelerate the oxidation process of your paint. Once the paint oxidizes, it will leave the paint looking dull and unattractive. Not only that, but dishwashing soap can wear out the exterior rubber surfaces on the car and damage the wax coating on your paint.