The section of the brain that controls human emotions is the amygdala. The amygdala controls every emotion, imaginable. Some people experience very dominant and prominent emotions given off by the amygdala. These irrational fears are called phobias, and they occur when the amygdala releases certain hormones that cause a particular level of anxiety or fear.
When I was younger I had acrophobia (fear of heights). Even when we went to Camp Snoopy (previously named) at the Mall or America my favorite "ride" was the escalator! However, as I got older (not necessarily grew up :)) I went to universal studios, six flags, valley fair etc. and I build up enough courage to go on the most extreme rides . Today, I don't even give heights a second thought. I believe that you are able to out grow your phobias because they "get old." In other words you stop believing that the same thing is frightening. Like after you watch a scary movie a couple of times, you know what is coming/what to expect. Heights are always going to be tall and far from the ground.
See I you have any of the top 10 phobias: