A rash on a penis can be caused by irritation, reaction to a detergent or soap, or infection by a sexually or non-sexually transmitted organism. Jun 12, · Itchy Foreskin And Moisture Under It. rash with red bumps above penis dry and sore but when im normal it's really moist and iv just realised that I. There are often no symptoms, but if symptoms appear, there may be an itchy rash on the penis. moist conditions; having a poor diet; Is it sexually transmitted?