[paul.fr]

Why do scars look different to normal skin under uv light?

[ukmicky]

Someone else will hopefully come along with give a better explanation but in general  like your blood  your skin contains cells  some of which are fluorescent which is why on CSI they look for body fluids blood etc under ultraviolet light. 

Fluorescent cells i believe absorb some of the energy of the UV light changing the wavelength of the light before its remitted (SOMETHING LIKE THAT).

And (I think) Scars contain less melanin than the surrounding skin which is why they don't tan and the lack of melanin in a scar means the level of fluorescent  cells differs between the two surfaces.

i think I'm only halfway there so as i said wait for a better explanation.