Smegma like substance. Moments if any?

Hi, My query is that few days back I had found a white like substance on my penis skin which I found out to be smegma which is common for every gender. But the thing I am concerned about is after cleaning it daily why does ut appears again and again...what is the general way to clean it? Secondly the major question I have is that while sleeping at night or even durinf daytime I fantasize some scenes of sexual pelasure which makes me aroused and this is done on regular basis for which I have got somd control over it by distracting myself but wanted to know that is it harmful for my penis that it gets erected for a longer time during night and daytime as well? Is the over occurence of smegma due to this unwanted fantasies? What should be a normal duration for fantasizing pleaure moments if any? Please help me an guide me through this. Thank you