What Causes Lego Bricks to Deteriorate?

[Bricked1980]

7 hours ago, Japanbuilder said:

So far the LEGO has held up but I worry about the hands on my minifigures getting brittle from holding accessories through all these weather changes. 

I've not had any problems as such with the Minifig hands going brittle, but I have got a couple of old figs where there arm sections have sort of cracked/split along the length of the arm from where the hands clip in to the socket on the arms. Not really sure why this would happen as I don't remember ever pulling the hands in and out of the arms when I was a kid. Something must have caused stress on the arm parts though for this to have happened.

Maybe it was something I did whilst playing with them as a kid. It's difficult to know whether general play has caused these problems many years ago or whether it's from some deterioration that has occurred whilst they've been in storage.