What Causes Lumps On The Shaft Of Penis?

I have had these bumps on the shaft of my penis for a VERY long time.. I am 18 years old and I have had them ever since I could remember.. I found out that they are called chicken-skin scrotum or something like that, and I cannot stand the fact that I have them... I have only had sex with my girlfriend, she is the only person I have lost my virginity to and we have been together for nearly 4 years but she doesn t seem to have a problem with them. Although she doesn t have a problem with them, I severely do. The bumps aggravate me and I feel ashamed to look at them, so I wanted to get some sort of surgery or something to remove them.. But I am scared because I don t know if it will cause major scarring and look worse than the actual bumps or give me erectile disfunction or what? I just really want them gone and I will do anything... Thanks