How to keep cases from getting dried out or how to somehow make them smooth again?

[Fenevar]

Today I received a new movie and was marveling at how smooth the case was, and how most of the cases of the movies on my shelves were more dried out, rough, unpleasant to the touch. I noticed this tendency a long time ago and had made an effort to make sure there was ample breathing space on each shelf for the movies so they wouldn't get so scuffed, but I still notice these tendencies with even newer movies. Is there a way I can periodically apply something to the cases to make them softer or to... I don't know, moisturize them or something?