Going for another (far fetched) reason for the darkening, could be that along with the oils from the skin,  maybe the finish has been worn down in those areas allowing for more UV rays to get to darken the wood? 
As I say, maybe far fetched but it's hard to tell from here.

No telling if the darkness will even out after sanding or not.  Could be some cherry stain in your future??

Figuring out how to do something you have never done is what makes a good challenge.