1. Duplicate the layer you want to work on.
  2. Change the blend mode of the new layer (Layer 1) to “overlay”
  3. Apply the “high pass” filter to layer 1 (located under layer/other/)
  4. Invert layer 1
  5. Lower the opacity of layer 1 and fine tune the amount of skin softening
  6. Add a layer mask to layer 1
  7. select the brush tool
  8. paint over the details in the face to hide the softening effect
  9. Paint away the effect from the rest of the image.

http://www.photoshopessentials.com/photo-editing/smooth-skin/