As far as Itching on penis is concerned, it is not necessarily a sexually transmitted disease. What may be the case be is that either you have developed some infection or allergy. Most commonly, a yeast formation or a bacterial infection causes itching on the shaft of the penis. What you need to do is to keep the hygiene and wash your pubic area with antiseptic soap. Also you can apply some medicated moisturising lotion and can apply on the penis. It will reduce the dryness and will probably reduce the dryness. Another thing which can be done is to wash your penis with salted water as it maintains the yeast balance.