There are many ways to smooth out complexions but if there are real
physical skin features (not just noise) that need to be smoothed then
blurring the AB channels is not going to do it. One of my favorite
techniques is to make a duplicate layer and run the median or dust and
scratches filter on the new layer with enough of a radius to smooth out
any defects. Option-click on the layer mask icon at the bottom of the
layers pallet to create a black layer mask thus hiding the newly blurred
layer completely. Now you can paint into the layer mask with white using
a soft airbrush, smoothing just those areas that require it.
You'll probably need to add some noise to the blur layer to match the
underlying layer - a small amount in the blur image should be enough to
kill any banding artifacts from the median filter as well. If you have
areas of skin highlights that approach white you might want to add the
noise in an overlay layer. Create a new layer and enable the overlay
apply mode. Fill this layer with 50% gray and group it with the
underlying blur layer. Now run the noise filter on this gray layer.
Noise is applied to the underlying smooth skin but ramps off as the
values approach white and black so you get cleaner highlights and shadow areas.