There is an explanation of how the microstructures have specific markers that are important to determining a person’s facial expressions. Luckily, they have figured out a way to map a high-resolution displacement map onto a surface to create a simulated version of our complex epidermis:
When skin stretches, the microstructure flattens out and the surface appears less rough as the reserves of tissue are called into action. Under compression, the microstructure bunches up, creating micro-furrows which exhibit anisotropic roughness…
We approximate the skin being flattened under stretching, and bunched up under compressions by convolving a 16K displacement map. We blur the microgeometry displacement map in the direction of stretching, and sharpen it in the direction of compression using the surface normal distribution histogram as a guide. This entire computation can be efficiently implemented on GPU shaders.
Source: gizmodo