Skin is not see-through because light that hits it is scattered by collagen as it passes through. It is analogous to trying to see in the fog with your car’s high beams — the light is scattered in all directions and much of it bounces right back at you.
In a brilliant experiment that borders on skin science fiction, a group of scientists from MIT used a holographic crystal to record the path that a light beam took through tissue to the other side. They then replayed it backwards through the tissue to recreate the original light beam. It would be like shining a light though the fog and having it come out as a straight beam on the other side. Cool, huh?
I don’t think this technique will allow you to see through the skin yet, but you could use it to direct a powerful light beam through the skin in such a way that it is not scattered, allowing for deeper skin cancers or other tumors to be targeted by light therapy.
It’s probably better that your skin isn’t transparent. Think of the painful organ sunburns after all.