What causes an iphone to be hot all the time?

How can you cool the phone down?

You are running too many apps at a time -especially ones that require constant communication, like GPS/direction apps. You also have some downloads running like movies, music, etc. Swipe out All your apps when you are done with them. If you have a 4s or 5s, they also have thermal overload problems - HOW to solve that is multi-step. Write back and let us know what model iPhone you have, before I write out the whole process for about the billionth time.