This is one of my favorite figure. A few days ago, I stumbled upon a facebook sale for the same figure (forgot to save the images and now I can't find it) where the plastic (except for the chest) turned yellow. The seller said that the figure was displayed in a smokefree environment with no direct UV light and that the parts he kept the box are still perfectly clear.

Fortunately enough, I moved six years ago and my figures are still boxed since (I had a lot of work to do in my new house and it will finally be finished by this summer) so my copy is still safe for now but knowing that someone who displayed it in safe condition for only 8 years had this issue is bothering me.

Is there anything I can do to prevent my copy from yellowing and still display it? Looking at what that seller said, I guess UV are not responsible for this. Maybe it's a reaction to something in the air? Should I try some kind varnish or something like that?