(Credits : The Soldier, by Ribeyrolles Leo)
Substance Painter supports Subsurface scattering both in its real-time viewport and in the Iray renderer.
Subsurface scattering is a mechanism of light when penetrating an object or a surface. Instead of being reflected, like metallic surfaces, a portion of the light is absorbed by the material and then scattered inside. This behavior is often known under the acronym SSS for "SubSurface Scattering". Many materials in real life have subsurface scattering such as skin or wax.
For further details, see the following pages :