Nipple question...

I noticed this prior to giving birth to my first child (who is 2 right now), and will try to explain it as best as possible so I don't have to take a picture. ? And this all may sound so dumb/confusing/crazy but I have no clue thanks in advance!
Okay, while looking at my nipples (which are pinkish in color) directly in the centers of them there are what looks like yellow/cream colored deposits or particles, that upon scratching lightly with my nail, will come out/off. Nothing is painful, or abnormal seeming about it, I'm just curious what the heck it is!!! 
Anyone have a clue/insight/similar issue?!