Subsurface scattering is having no effect

White_wizard

I am not sure why subsurface scattering seems to be having no effect on my hair

White_wizard

I changed the scale in the scene, however, the subsurface is only affecting the characters skin and not his hair, any idea why? 

EarthQuake

Certain effects like translucency need direct lights in the scene, so if you only have a sky light active, try adding some additional lights.