Yeah, it’s the effect you get when you hold up your hand to a light and you can see a red tinge in the thinner parts, it’s how light goes into some materials and the effect that creates. If you do a google search on Mental Ray Skin Material or Vray Skin Material you’ll see what that type of thing looks like and how they have several textures to create the layers of the skin.
For games, it can’t quite get there yet so there’s only just the backscatter color and not much control over it so for a game most of the skin texture has to be in the diffuse texture