>>1013569
2d artists have their own exotic techniques to paint skin from scratch for custom look, but in general, and especially in 3d, anything that has repetitive microdetail or repetitive randomized detail is better done with procedural base (basically math functions like voronoi noise composed together) and some manual painting of extra detail on top of it. You can use premade procedural base or generate one yourself in shader nodes / substance designer / material maker / whatever if you want more advanced control.