The mixing brush tool is one of the most underutilized tools in portrait retouching. When used correctly, the mixing brush tool can be used to blend blotchy skin together, fix makeup in areas where a makeup artist may have missed applying makeup, etc. Here is a quick introduction to using the mixing brush as a portrait photographer.
In order to use the mixer brush tool correctly, you’ll want to separate the skin texture from the skin color so that you’re not distorting skin texture. Because the mixer brush tool is used to blend colors together, you’ll loose all skin detail if you do not separate those two elements onto two separate layers, with the frequency separation technique. If you still don’t know how to do that, fear not, here’s a quick introduction on the frequency separation technique that I created a year ago:
If you would rather skip replicating that process all together, I have a couple of free retouching actions available HERE.
Here's a before and after: