Many skin shaders built before SSS, GC, and IDL were available use built-in glow to account for missing scatter, ambient, and bounced light as well as a complete misunderstanding of how to do linear color processing workflow.

You can confirm this by rendering with all lights sources turned off. If you see anything but pure black, you have a glowing shader doing old-school compensations. It makes it impossible to get full contrast since the skin never goes black no matter what.

Look for use of the ambient channel in the shader, or the use of hard-coded color jammed into Alternate_Diffuse, which is supposed to have a lighting node plugged in there, but often does not.

 

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)