there are many different things that could cause something like this. it could range from something tiny like a rash or a new washing powder to an infection or at a tiny chance TC. a possible symptom and one men don't like to talk about, excessive masturbation. ask him how much he masturbates. try to get him to stop for about a week and see what happens. if there isn't a difference then go to your doctor straight away, its better to be safe than sorry.