Is it bad for my iphone charger to be used all the time?

My sister and I have an iphone 4 and she also has an ipod touch (4th generation). I charge my phone about once or twice a day depending on how much battery i drain. The problem is, my sister breaks her chargers all the time and she tends to use mine to charge BOTH her apple products which takes maybe a few hours. So when i want to charge my phone, the charger gets hot and i don't know if that is bad or not. Should I be worried whether or not the charger gets hot or am I just paranoid?

It's not a big deal, but it does mean you have an inefficient charge if it's getting hot, and you're probably wasting money

If the charger or the phone heats up while its charging, then you are using energy faster than it can be replenished. The charger shouldnt be a problem in your situation, but (personal recommendation) don't use your phone while it is charging. It damages the battery