What you are looking for is a material system that does the work of geometry. To do accurate skin you want to set up the layers (like a human body is setup), however this ignores that the human body takes up actual mass and each layer has a real geometrical thickness, stacked one inside another -- much like a matryoshka doll. This "layer thickness/stacking" would have to be modeled in your host application to be rendered correctly in Maxwell (as it stands currently).
There is no way to stack up real thickness (or virtual ones either) within the current Maxwell material system -- this affects more than just skin, it also affects things like coatings which often have to be stacked at specific thicknesses to achieve anti-reflective effects (like you might commonly find on a camera lens or a pair of glasses).
This is an excellent request and I have made similar ones repeatedly so +1
In the meantime you can get "reasonable" results using Thins SSS as I show here:
viewtopic.php?f=48&t=38386Best,
Jason.