Simulating scattering at this complexity is probably excessive, but realistic rendering requires modeling at least two distinct layers below the oily layer responsible for specular reflection.
Real skin is even more complex medically, the epidermis alone is considered to contain five distinct layers (Poirer 2004). Graphics researchers have produced very detailed models that describe optical scattering in skin using as many as five separate layers (Krishnaswamy and Baranoski 2004).
Complicating the process further, multiple layers within the skin actually absorb and scatter light differently, as shown in Figure 14-4.
