In this case, a salad dressing makes up of an oil-and-vinegar heterogeneous mixture as long as if it is let to stand it is possible to decant its constituents by density difference, therefore, we do not mind about the polarity of the different ingredients. The only necessity is a well shaking before its use.
So that they combine smoothly and you aren't left with separated looking salad dressing. With polarity only, like-polarities dissolve like-polarities. So you must make sure that all your ingredients are polar or all are nonpolar.
