Oil seeping from mbp keys? I have a pretty recent macbook pro 15in, aluminum unibody, probably not yet one year old.

It mainly gets used in clamshell mode connected to an external monitor.  I've noticed frequently now when I take it out for use as a proper laptop, the left side Option and Command keys have an oily substance seeping out of them, with a corresponding spot on the screen where it touches those keys when closed.

Any ideas on what's causing this?
Sounds like oil from your hands to be honest