Read up on masks. It is exactly what it says. It masks the areas that you don't want the effect / adjustment to be made. Search on quick mask on google for tutorials.
What I sometimes do, is to duplicate the layer. Then I apply the effect to the layer, second from top. You can then delete the area you want to change, on the top layer, with a soft brush. You will then see the effect in the deleted areas.
Ended up selecting the hair area. Create new image. Paste, apply effect, shift+ctrl+c, went to original, paste, positioned it.