He has some kind of irritation and itchyness in his penis what can it be? knowing he has been sexually active

Irritation: Tough to say without an examination of the penis. Could be a dermatitis of the penis, or some other issue. Best to have the area examined to be diagnosed and then treated best. Good luck.

See answer: Assuming no external lesions on penis, an irritation or "itchy" sensation inside the penis usually related to an irritation and/or inflammation of the urethra or prostate which may be infectious or not. STD-related urethritis is usually associated with burning upon urination, urethral, discharge, and white cells on urinalysis and caused by chlamydia, gonorrhea, or trichomonas. Recommend MD visit.