Insulin going bad

I use pens for my insulin and I've heard that if it reaches a certain temperature, it can go bad...has anyone had experiences with this? And if so, how do you know, do you get sick or does it visually go bad. Also, I read on the package that you are supposed to use it within 30 days of opening a new pen, is it a big deal if you go more than 30 days using the same opened pen?

I think that it just becomes less effective or ineffective. If you notice that you have less control towards the end of the 30 days it could be because the insulin is getting old. Perhaps if you could keep it in the fridge it would last longer but that isn't always possible on a pen being used.