moisture forming on blu-ray discs...???

[cramped_misfit90]

First let me say, I copy all my BDs and put away my official BDs in a new CD case in my closet. For years I've had a very weird occurrence with a few blu-ray discs... after owning the discs for about a year I get the official BD out and look at the bottom of the disc, dots of moisture has formed and dried. Only a few has done this... Why is this happening???