Household cleaning products – dishwashing detergent being the most common culprit – are specifically designed to do things that are bad for automobiles. In the case of dish soap, it’s designed to break down fats and sticky greases on your dishes: because automotive wax is essentially a grease, that dish soap will strip the wax coating you want on your paint, leaving it with little shine and no protection. Also, some household detergents have a micro-fine abrasive in them – these can permanently scratch your car’s paint’s surface. Always use a high-quality commercial liquid car-wash soap, which should be formulated to remove dirt and grime without affecting your car’s essential coatings. The same goes for any other car cleaning – use car-cleaning products.