Subsurface scattering (SSS) is an effect to give transparent objects, like skin or candle wax, a more transparent look. Light can pass through objects to light the back side or return to the surface to help give off a glow, much like a glowing candle.
Update: SSS is texture dependent (Specifically the skin textures). Hence you if you find that something looks off, you might need to tweak these settings to match what you are using. It is not possible for a single set of values to look good with every texture. By Aiyen
This parameter determines the overall performance and quality of SSS. For changes to take effect from this parameter, users must save and apply the new values in the GUI. (Reference)
Quality=(0, 1, 2)
This determines the distance at which SSS starts to show up on characters and objects that use it. This should be left where the ENB Profile has it set, since the author has it balanced accordingly.
This parameter is the actual amount of SSS that is calculated in game. Raising this number above "1.0" is not recommended, and may look bad in game causing neck seem issues.
The parameter is light upper layer use, mimicking the upper layers of skin having brighter semi-transparency and it differs from lower skin layers that have blood and flesh underneath. Not used by objects like wax candles or milk.
This parameter is the type translucency that a material has to light, to simulate light passing through a transparent or semitransparent object.
Both the next two parameter work the same by applying saturation to the diffuse texture of the models. Normal skin color will turn to red, and it is recommended to only use SubdermalDiffuseSaturation as it fits better with skin lighting.
This parameter is how SSS is blended with vanilla skin and subdermal lighting. Epidermal lighting is applied after the subdermal lighting, so these values tend to be more than the epidermal values.
This parameter does not work like the above EpidermalMix, instead low values here let light go through objects to be lit only on back side. Higher values will return more light back to the surface of the object, and gives skin less realistic look. Recommended to keep this setting low and compensate with SubdermalAmount.