There is much written both on the web and in holistic books about castor oil.
The reason two oils are used.....castor oil goes in deep and the lighter oil either olive or another light oil brings the debris to the surface.Another good point...this combination smooths out any surface blemish.

one great tip for hands...most girls in my youth did this before a spoon olive oil followed by a teaspoon sugar massaged into hands...rinse well of course.
try it!!