Why are some apples coated with artificial wax?

After harvest, apples are washed and brushed to remove leaves and field dirt. Because cleaning removes the fruit's original wax coating, many apple packers apply a commercial wax to protect the fruit. These waxes aren't harmful. They are made from edible plant materials and help to prevent dehydration and accessibility to microorganism.
 
There’s no reason to, but. if you wish to remove this wax before eating the apple, you may have a difficult time. This is because the new wax adheres to any remaining natural wax.  Your best bet is to scrub apples with a vegetable brush in lukewarm water prior to using them.
 
Source(s):
U.S. Apple Association "Apples and Wax"