As we cannot use the Dirt shader for animations, you have to generate a Dirt map. For the Dirt map calculation you have to unwrap and unfold the UV mesh of your object first. As this can be a very time consuming process in bodypaint 3D, you should avoid high resolution meshes. Try to use a combination of low polygon objects with HyperNURBS objects.
by Peter Hofmann aka peXel
Software: Cinema 4D