minoxidil will only have a significant effect on the areas to which it is applied.
minoxidil does get absorbed systemically, and therefore even when applied topically does effect hair all over your body. However these effects, while sometimes noticeable to the trained eye, are generally very small.
You should see the hair on the back of my f*****g neck. The primate connection in our genes is making itself all to noticeable thanks to minoxidil. I have to shave that crap off every two weeks!