Skin shading with Mentalray in Maya

Needed MentalRay shaders:
Get the Maya files for Diffusion here
Download example scene here.

This is not a finished "perfect skin shader" but a work in progress tutorial
on how to build your own skin shader.

The core of this shader network is the mix8layer shader by Francesca Luce.
It works like layers in photoshop with color correction and different blending modes.
It helps when building advanced shader networks.
Use it as your objects material and connect the other shaders or textures to it.

To get the "translucent" feel of skin I´m using the Diffusion Sub Surface Scatter shader by Daniel Rind (thebigMuh).
Create a Diffusion node and lower the Direct and indirect scatter attributes to
something in the range of 0.2 - 0.4 depending on how strong effect you want.
Raise the samples to at least 16 for a less grainy look.
(Higher values take more time to render so use a low value like 8 while tweeking.)
Attach the Diffusion shader to the mix8layer shader as base material.

The next thing is a Phong E shader with a skin color or texture attached.
Raise the Roughness setting and lower the specular color to get that broad soft highlight.
You should also set the Reflectivity to 0.
Attach it to the mix8layer shader with Add as Blending mode.

Finally the bumpmap. In this example I´m using a noise texture
but you could use a painted bumpmap for more accuracy.
The outermost layer of skin is very transparent and to get that effect I use a Blinn material
with full transparency and a bumpmap attached.
Try using a Phong or Phong E shader for a slightly different result.
Attach the blinn to the mix8layer shader with an Add Blend mode.

To get the Diffusion shader to use the bumpmap for more correct shading
I connected the bumptexture through a reverse -> set range.
(With old max set to 1 and a low value like 0.1 for max. This could be different depending on your bumpmap.)
Set range -> luminance -> Diffusion parameter of the Diffusion shader.

Well thats it. As I said this is not a finished skin shader but more of a concept to add your own touch to.
Try adding more layers like maybe a separate painted/photo skin texture layer or
a Dirtmap shader (also by Daniel Rind) layer with a dark redbrown Dirt color to give the shadows a little red tint.
Keep experimenting!

Here you can see the different layers rendered separately.
The effect is a bit strong just to make it more visible.

Good luck!