Masks of Imperfection
Skin retouching, when done by hand, requires tiny little adjustments of luminosity everywhere it’s necessary. Pixels can be locally brightened (dodged) or darkened (burned) using a curves adjustment layer for instance, with a layer mask. This is one of the cleanest way to fix blotchy areas without damaging the skin texture, but it can take a lot of time in some cases.
These pictures are a representation of this method. Blue means lighter, red darker.