Simulating this phenomenon is calculation intensive and until now has only been available in high-end renderers. Even then, it can take several minutes and even hours to render a single frame using subsurface scattering. Now, with the new subsurface scattering node in ShaderFX 1.5, you can apply this effect to your model and see it rendered in real-time in 3ds Max's viewport.

To achieve this effect, the subsuface scattering node renders the diffuse light of the object into an off-screen buffer. The buffer texture is blurred, and finally wrapped back around the model. All of this happens automatically. This process blurs the lighting and makes it look like it's being scattered below the surface.