Subsurface Scattering
Light entering and bouncing inside a material
Also known as: SSS · Subsurface
Definition
Subsurface scattering (SSS) simulates how light enters a translucent material — skin, wax, marble, leaves, milk — bounces around inside, and re-emerges at a slightly different point. It is what makes a hand backlit by sunlight glow reddish at the fingertips, or marble appear to have depth instead of just being a coloured surface. Real-time SSS is expensive but essential for believable skin shading in characters.
In production
UE5 ships a Subsurface Profile shading model with separate radius and tint controls per character, letting artists set distinct scattering behaviour for skin versus, say, a translucent ear where light passes through more directly. For mobile/lower-end targets, a cheap approximation is fake SSS via a wrapped-lambert term added to Emissive, avoiding the cost of the full screen-space diffusion pass higher-end platforms use. Unity's HDRP implements a similar Diffusion Profile asset, with a "Transmission Mask" that lets thin geometry like ears or leaves transmit light from behind. A common mistake is applying the same SSS profile to every character regardless of skin tone or thickness — the scattering radius should scale with material density, since a default profile will look waxy on thin surfaces like eyelids without tuning.